a phosphorus-31 nuclear magnetic resonance spectroscopic study of complexes of zinc with some...

A phosphorus-31 nuclear magnetic resoilailce spectroscopic study of complexes of zinc with some phosphine oxides, sulfides, and selenides'

P I I I L I P A. W . D L ; \ N ~ A N D GI'.I:TI-IA K . CAIISON Dcl)cr~.t~rre~~t (!/'Chor~ist~;v, Urli\.e~..sit!, 01' II'c.srer.r~ 011to/.io, Lorltlorl. O I I ~ . . Canelc/o N6A 5.87

l1cccivccl Dcccmbcr 20. 1982

PHII.II' A. W. DEAK and GI:I:TIIA K CAIISON. Can. J . Chcrn. 61. 1800 (1983). Zn(SbF,,)2 in licluicl SO2 has bccn shown to act as an acceptor towartls a variety of pliospliine oxides. suifidcs, ancl sclcnitlcs,

forming cornplcxcs which have bccn chal-actcrizcd in solution using "P nmr. Slow-exchange "I' nmr spcctlx arc reported for the complcxcs Z ~ L , , " ( t i = 6, I,? = Ph2P(0)CH2P(O)PhZ or Li = ( P ~ ~ P ( O ) ( C H ~ ) ~ ) ~ P ( O ) P I I ; Ir = 4. L2 = PhrP(E)CHIP(E)Ph2 (E = 0, S , or Sc) or bitlo~tntc~ (Ph2P(E)CH2);CMc ( E = S or Sc). or L = (C,,HI ,),PE (E = 0. S , or Sc) or RiPE (E = S or Sc. K = PI1 or o-C,,H.,Mc); 11 = 3, Li = ( P I I , P ( E ) ( C H ~ ) , ) ~ P ( E ) P ~ ( E = S or Sc) or L = RIPE ( E = S or Sc, I1 = C,,Hl l , Ph. 01- o-C,,H.,Mc); 11 = 2. L = R3PE ( E = S or Sc. I 1 = o-C,,H,Mc or, perhaps, C,,Hll): 11 = I (possibly), L = (0-C,,H,McI)PS), and partial spectra for IZn(ScP(C,HI,),),(SP(C,,H,,)),, ,I2.' (11 = 3 or 4). N o cvidcncc was fountl for the mixctl oxidc- chalcogcniclc species [Zn(EP(C,H, l) j) ,(OP(C,,HI , 1 " . 111 most cases the "P ninl- spectra arc very similar to those rcportctl earlier for the corresponding c~idmil~m complcxcs. However. in most instances wlicrc comparison could be matlc i t was fountl that the rate of intcrmolccul;u. lig~intl cxchangc ~ v a s lcss for the zinc complexes than for their catlmium counter-parts, (Complcxcs with (Ph2P(0)(CH,)r )2P(O)P1~ and P I I ~ P ( O ) ( C H ~ ) ~ I ' ( O ) P ~ , arc cxccptionnl in being more labile for zinc than catlrniurn. )

PI-lltlr> A. W . DEAN ct GI.:E~'I~IA K . C,\RSON. Can. J . Clicm. 61, 1800 (1983). On rnontrc quc ic Zn(SbF,,)? clans clu SO, licluidc agit commc un acceptcur cnvcrs divers oxytlcs clc phosphinc, dc sul f~i~-c

ct dc sdldniurc. en formant dcs complcxcs q ~ ~ c I'on a c;u.actCrisCs en sol~ition par la rmn tlu "P. On ~xpportc Ics spcctrcs tlc I-mn du "P cl'dehnngc Icnt dcs complexes dc Z~L, , " (11 = 6, L, = Ph2P(0)CHIP(O)Pli2 o u L; = ( P I I ~ P ( O ) ( C H ~ ) ~ ) ~ P ( O ) P ~ : 11 = 4, LL = Pli2P(E)CH2P(E)Ph2 (E = 0. S OLI Sc) ou biderttotc,. (Ph2P(E)CH2),CMc (E = S ou Sc), ou L = (CbHll ) ,PE ( E = 0, S ou Sc) ou RIPE (E = S ou Sc, K = PI1 ou o-C,H,Mc); 11 = 3. L; = (Pli ,P(E)(CH2)2)2P(E)Pl~ ( E = S ou Sc) ou L = R'PE (E = S ou Sc. R = C , H I 1 , Ph ou o-C(,H,Mc); 11 = 2. L = R;PE (1: := S o u Sc, R = o-C,,H,Mc ou pcut etrc C,,HI ,); 11 = I (possiblc~ncnt), L = (0-C,H,Mc);PS) ct Ics spcctrcs particls dc [Zn(Scf'(C,,HI I)3),(Sf'(C,,Hll ).I),, , 1 , ' (11 = 3 ou 4) . On n'a pas pu prouvcr I'cxistcncc d'cspCccs rnixtcs du type oxydc-chalcog6ni~1r-c: ~Zn(Ef'(C,,H,I).I),(OP(C,,Hll ) ; ) , ., 1'~'. Dnns la plupart dcs cas Ics spcctrcs dc rmn tlu "P sont trts scmblnblcs h ccux ~ p p o s t e s ;~ntCsicurcrncnt pour Ics complcxcs corrcspondants du cntlmium. Ccpcntlant dans la plupart tlcs cas. ou i l cst possible ti'Ctablir line cornparaison. on trouvc quc la vitcssc tl'dcliangc intcrmoldculairc dc lig;md cst plus f;~iblc dans Ic cas du zinc cl~ic dans Ic cas tlcs complcxcs corrcspondnnts tlu catlmium. (Lcs complcxcs avcc (Pl i~P(0)(CH21~12P(O)Pl~ ct Ph2P(0)(CH2)2P(O)PIi2 sont cxccptionncls en cc scns clu'ils sont plus labilcs dans Ic cas du zinc clue dans Ic cas tlu cadmium.)

['l'ratluit pxr Ic journal 1

Introduction In earlier work from this laboratory ( 1 . 2) , i t was shown that

a wide variety of new con~plexes of cadmium with phosphine oxides, sulfides, and selenides could be prepared from Cd(MF,)? (M = As or Sb) with the appropriate ligand in liquid SO2. The M F , anions and the solvent SO? are very weak donors so that coordination by the ligand(s) of interest is facil- itated in these systems. Phosphorus-3 I nmr proved a ~ ~ s e f u l tool to characterize the complexes, a selection of which then pro- vided the basis for a 'I3Cd nmr study of species containing these model Group VIA donor ligands (3). A helpful feature of both the "P and the "'Cd nlnr spectra of the c a d m i ~ ~ m conlplexes is the occurrence of two-bond "'C~-E-~'P (E = 0 , S , or Se) nuclear spin-spin coupling which is readily observable for E = S or Se ( 1 , 2) and observable with ""d enrichment for E = 0 (3). The splitting patterns observed in the "'Cd nmr spectra both allow unanlbiguous assignment of these and con- firm the interpretation of the "P nmr spectra.

With the "P and metal nmr spectra of the cadmium complexes in hand, we felt it would be instructive to measure analogous spectra of some related zinc complexes for conl- parison. As the first part of our study we have measured "P nmr spectra for a range of the title con~plexes, and report them here. Zinc-67 (4.1% natural abundance, spin I = 512) is a quadru-

'No reprints available. ' ~ d d r c s s corrcsporldcnce to this author

polar nucleus and so the "P nmr spectra of the zinc con~plexes contain no observable "z~-E-~~P spin coupling. In them- selves they are thus not as informative as those of their cadmium analogs. However. with a priol. knowledge of the spectra of the cadmiuni complexes the spectra of the zinc conlplexes can be assigned with some confidence, as we show.

To our knowledge, there have been no previous "P nrnr studies of complexes of zinc with phosphine sulfides or selenides, perhaps because of the difficulty of interpreting an isolated spectrum (see above). However. zinc conlplexes with phosphine selenides and, particularly, phosphine sulfides are well-established. Most involve zinc halides and are of the type ZnX?. L? where L represents a donor with one P=S (or Se) donor site or L? a donor with two such sites (eg. refs. 4- 10). The complexes 2ZnX2. Ph3PSe (X = CI or Br) have also been reported ( 1 I ) , as have the species [ZnL4](C104)2 (L = SePMe, (6) or L, = dppnlS: (12)), which demonstrate the importance of the nature of the anion in n~axiinizing the number of ligands that can be bound.'

Zinc complexes with phosphine oxides and related phosphoryl donor ligands have been a topic of extensive interest, though relatively few 31P nmr investigations have been reported

'Abbreviations used in this paper: Cy = c-C,HII ; o-to1 = (I-

C,H,Mc: dppmEz = Ph2P(E)CH2P(E)Ph2; dppcO? = Ph2P(0)(CHZ)2- P(O)Ph2; tripodE3 = McC(CH2P(E)Ph,),: triphosE3 = PhP(E)((CHL)?- P(E)Ph?)?; TTA = tlicnoyltrifluoroacctonate (1 -).

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D E A N A N D CARSON I So 1

(see below). The most important types of complexes known are: ZnL?X? (L = ligand with one P=O donor site or Lz =

ligand with two P=O donor sites, X = coordinating anion) (e.g. refs. 13- 17), [ZnL,]X2 ( L = ligand with one P=O donor site or L? = ligand with two P=O clonor sites; X = weakly coordinating anion) (e .g. refs. 13- 15, 17-20), [ZnLS]X2 ( L = ligand with one P=O donor site; X = weakly coordinating anion) (e.g. refs. 19, 21, 22), and [ZnL6]X2 ( L = (HOCH?),P=O, X = ClO,- (23); L? = ligi~nd with two P=O donor sites, X = weakly coordinating anion (e .g. refs. 14, 24); L3 = ligand with three P=O donor sites; X = weakly coordinating anion (e.g. ref. 25)).

A few "P nnir data are available for zinc coniplexes of phosphine oxides. In an early application of j l P nmr, Walker and Li (26) used j 'P niiir to determine the formation constant (10 L mol- ' ) of the (isolable) 1 : I complex Zn(TTA),. OP(II-C~HI,), in CCI, at 299 K. More recently, ligand exchange with excess free ligand was found to be fast on the "P nmr timescale at ambient probe temperature for both Z ~ ( O P B U " ~ ) , " in DMSO and Zn(dppmO?)CI? in CH'Cl? (15); from the position of the single exchange-averaged resonance observed in these cases, it was deduced that ligand dissociation is significant for the former system, but not for the latter. Lincoln and co-workers were able to reach the slow exchange region of the reduced temperature j 'P nmr spectrum for Zn(OP(NMe2)3),? ' -OP(NMe?), ( 19) and Zn(OPPh3),' ' - OPPh? (20) mixtures in CD?Cl?, but not for Z ~ L ~ ? ' - L (L = OP(OMe)l or OPMe(OMe)?) mixtures in the same solvent (19). In all these previous "P nmr studies of phosphoryl donor ligands sizeable positive values of the co~nplexation

- shift, h6p (= ?II>, con,plu.i ?IP, I.rcc Ilg;,l,d) were found.

Experimental Morericrls

Zinc hexafluoroantimonatc, Zn(SbF,)?, was synthesized by thc l i t - craturc method (27). The ligands were prepared, and sulfur dioxidc dried. as reported earlier ( 1 -3. 78).

Mcrr1iprt1atiori.s All transfers of the cxtrcmcly moisture-sensitive Zn(SbF,), were

carried out in a dry-nitrogen filled glovebox in which the atmosphere was maintained by circulation through liquid nitrogen cooled traps. Similarly all weighings were carried out in the glovcbox. Sulfur di- oxide was added to thc nmr samples outside the box from a calibrated glass and Teflon vacuum line.

Pl~ospl~orrrs-31 rlrrit. spectrcr Nuclear magnetic resonance samples were prepared in flame-sealed

hand made 10 mm od nmr tubes, and 40.54 MHz 'P-{'H) nmr spectra measured using an XL- 100- 12 spectrometer system, as de- scribed before ( 1 , 2, 28). The "P nmr chemical shifts are given relative to external OP(OMe)l in (CD3)ZC0, used as a reference/lock substance, in the annulus between the I0 mm tubes and a standard 12 mm od nmr tube; approximate conversion to H3P0, (at 308 K) as reference is 801~toMelJ,~x,l = SH3p0,(cxII - 1.7 ppln Shifts to higher frequency than the reference are taken as positive. We estimate that S1, and values of l ~ ( " p - ~ ~ S e ) have maximum errors of t 0 . 1 ppm and t 2 Hz, respectively, as in ref. 2.

TABLE I . "P nmr spectral pararnctcrs of somc zinc complcscs witti phosphine oxiclcs

7' S,>" Abp<' Complcx" (K) (ppm) (ppml

"Cy = c-C,,HII: tlppniO, = Ph,P(O)CH~P(O)Pli,: tr~pllosO, = PhP(0)- ((CH.I,P(O)PII,),. - " M ~ ~ s L I I - c d relative rtr cxtcl-nal O P ( O M C ) ~ in (CD,),CO: 6,,,,,~,~l,,i,,,,, - 611,11, , , , , - 1 .7 pp111; positive c l~cn~ical shifts ;ire to lhiplier frcquc~lcy than the reference; estimated error in mca.;urcmcnt ?0. I ppm or Icss.

'A6, , = 61~(complcu) - Gl,(frce lipand). "Slow cxchanpe witli cxccss free lig;~~id at 209 and 308 K . '6,, and v , , , for h-ce OPCy, tlcpcnd niarkcdly on temperature and solute

concentration. 'Slow ligand exchange between 3: 1 and 2 : 1 cornplcxcs at 209 ;111d 308 K . 'Slow exchange witli excess frcc ligand at 201 K, intcrlncdiatc cxchangc at

308 K ; the resonances B ant1 C appear to be collapsing (intl.arnolcc~~Ix cx- cIi;lnge) bcforc intermolecular cxchangc bccolncs rapid (cf. ref. I ).

''A = nun-terminal phosphorus atom. B and C = terminal phosphorus atom; J ( A B ) = 7 Hz: J ( A C ) ; ~ n d J(BC1 are not obscrvcd.

attributed to Zn(OPCy,),?'. The "P chemical shift of this complex, and hence its complexation shift, both given in Table I , are very similar to the 62.4 ppm (6 .9 ppm) found for the cadmium analog (3). Evidently Zn(OPCy3),". like Cd(OPCy3)," (3) , but unlike other Zn(OPR3)," (R = BLI" (15). NMe2 (19) , or Ph ( l o ) ) , undergoes slow ligand exchange with excess free ligand at ambient probe temperature. A cheni- ical dissimilarity between Zn"-OPCyj and Cd"-OPCyj mixtures concerns the formation of poorly soluble M(OPCy,),- (SbF6)?. This is formed in cadniiun1-rich mixtures but not in zinc-rich mixtures; in the latter case Zn'! (solv.) and Zn(OPCy,)," seem to coexist in solution.

Slow exchange "P nmr spectra are found at 308 K or below for Zn(SbF6)?-dppm0: mixtures over a range of L/Zn., When L/Zn > 3 the spectra show two lines. The more shielded signal, attributable to excess free ligand, disappears at L / Z n = = 3 so that the highest con~plex formed is Zn(dppmOz)3' ' which, by analogy with Zn(triphosO,)?' ' (see below), probably contains an octahedral ZnO, core. When L/Zn < 3 a second species is formed which does not exchange ligands with the 3 : 1 complex at an nmr-detectable rate; its "P resonance is deshielded from that of Zn(dppmO,),?' and becomes predominant at L/Zn -- 2. Hence the second zinc complex is Zn(dppmO2)?'+. Details of the "P nlnr spectra of the dpplnOz complexes are included in Table 1. The "P chemical shift of the 3 : 1 complex is similar to that of Cd(dppm02)32' (34.5 ppm) which also exchanges slowly on the nmr timescale with excess free ligand at ambient probe temperature (1). How- ever, the "P nmr chemical shift (and coniplexation shift)

Results and discussion of Z n ( d p p n 1 0 ~ ) ~ ' ~ are significantly larger than found for

Complexes ofphospkine 0-rides 'The slow exchange "P nmr spectra observed for complexes of Zn(SbF6)1 and 0PCy.3 two "P nmr Zn(SbF& and dppni0, in SO, at ambient probe temperature contrasts

resonances at ambient or reduced temperature when O P C Y , / Z ~ with the fast exchange spcctra observed for ZnCI?. dppm02-dppniO1 > 4. The more shielded of these is from excess free ligand and mixtures in CH,CI, (15). This behaviour is consistent with the order by studying the mixtures as a function of L/Zn the other can be of Lewis acidity Zn(SbF,), > ZnCI,.

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1802 CAN. J . CI-IEbl. V O L 61. 1'183

Cd(dppm02)2'i (36.8 ppm (9.6 ppm) at 220 K ( I ) ) . In aciclition, ligand exchange in Cd(dppmO,)," -Cd(dppm02);" mixturcs is fast at ambient probe temperature unlike the bchavious found here for thc zinc complexes. A plausible explanation for these differences lies in the larger size of the cadmium ion: this should f r ~ v o ~ ~ s solvent and/or anion coorctination to Cd(dppmO?)," (albeit short-lived to be consistent with the "P nmr spectra) and lead to a lower Lewis acidity at Cd and hence, probably, a smaller AS1,; i t should also favour what appears to be an SIi2 exchangc process between the 2 : 1 ant1 3 : 1 complexes.

At 204 K. samples containing triphos03/Zn > 2 give a slow exchange j lP n111r spectrunl consisting of the partly super- imposed spectra of excess free triphosOz and a 2: 1 complex, Z n ( t r i p h o ~ 0 ~ ) ~ " . The spectrum of the 2 : 1 complex consists of three equally intense regions of resonance labelled A, B, and C in Table I . As the temperature is raised, B ancl C begin collapsing together but intermolecular exchange with free ligand starts to occur before this process is complete and results in 21 broadened spectrum at 308 K. Nevertheless B and C can be assigned to the coordinated -Ph2P(0) groups and hence C to the coordinated -PhP(O)- group of a cornplexed triphos03. Overall this spectrum resembles that of Cd- (triphos03)2" for which an s:fciilc. structure has been suggested (I) , . ' and so we tentatively assign the zinc complex the same structure. In these species the inequivalence of the terminal phosphoryl sites is thought to arise from the particular ligand conforrnation frozen out at low temperature ( I ) . The lability of the zinc complex at ambient probe temperature is in contrast to the slow intermolecular exchange found for Cd(triPhos03)?" - triphoso, mixtures under the same conditions ( I ) . The same order of lability, Zn > Cd, holds ibr complexes of Ph'P- (0)(CH2)?P(O)Ph2: we could not obtain slow exchange ."P nrnr spectra of any Zn" -dppeO, mixtures at any accessible temperature (though ASIJ(ave) was significant), whereas slow exchange spectra have been measured for Cd" -dppe02 mixtures at reduced temperature ( I ) . Possibly the bite of the seven- membered chelate ring gives a worse fit on Zn" than on the larger Cd", resulting in labilization of the zinc co~nplexes relative to the cadmium complexes.

Cotnplc,res with j~hosphit~c sic1ficle.s At 199 K the j lP nrnr spectra of SO2 solutions in which

dppmS,/Zn(SbF,), > 2 exhibit two signals. The more shielded of these is due to excess free dppmS? and variation of the L/M ratio shows that the less shielded arises from the 2 : 1 complex Zn(dppmS2)z"-. This species has been isolated pre- viously (12) and is now shown to exist in undissociated form in solution under the conditions of our experiment. The nrnr spectral parameters of the complex are given in Table 2. As the temperature is increased from 199 K the signals from samples containing Zn(dppmSz)l?+ and excess dpprnS? broaden and eventually, close to ambient probe temperature. collapse to a single exchange-averaged signal. Clearly ligand exchange between free and bound dpprnS2 is rapid on the nmr timescale at or near 308 K. Overall, however, the zinc conlplex is less labile than its cadmium analog for which slow exchange jlP nmr spectra could not be obtained under any conditions ( I ) .

' ~ n .\-jac. structurc is also favoured for thc co~nplcx Zn(L L L)," of the tr~dentate phosphoryl donor ligand (Mc,N),P(O)NMcP(O)- (NMC,)NM~P(O)(NM~~)~ (25); this is the only othcr related spccies we are aware of.

TABLE 2. "P nrnr spcctl-al parameters of somc zinc - phosphinc sulfitlc complcxcs, zn(SPK;),,-", in liq~~itl SO2 at 209 K

11 in S,," AS; SPR," zn(SPRI I,," (ppnl) ( P P ~

SPPh, SPPh, SP(0-tol), SP(0-tol), SP(0-tol), SP(0-tol), SPCy, SPCy, SPCy, dpplnS2/2'

"o-to1 = o-C,,H.,Mc; Cy = c-C,,H~,: dppmS1 = Pli2P(S)CH?P(S)Pli1. - "Measured relative tu external OP(OMc), in (CD,),CO; ti,,,, ,,,,,,,,,,,,, - ti,,,,.,,,,,,,, - 1 .7 ppm; positive clic~iiical shifts arc to higher frequency than the rcfcrcnce; cstim;ktctl error in mc;lsurerncnt to. I ppm or Icss.

' Ati,, = S,,(complcx) - ti,,(frcc ligand). "Slow cxcliange with excess free ligand at 209 K. intermediate exchange at

308 K. "Slow ligantl cxchangc bctwccn 4 : 1 and 3 : 1 complcxes at 209 K. fast

exchange at 308 K . 'Slow lig;~r~d cxchangc bctwccn 4 : 1 end 3 : 1 complexes at 209 K. intcr-

rncdiatc cxchangc at 308 K. "low ligand cxchangc betwccn 3 : 1 and 2 : 1 coinplexcs at 709 K , fast

cxchangc at 308 K. "Slow ligand exchange in mixturcs of 3 : 1 . 2: 1 , and I : I ( ? ) complexes at

209 K, Fast cxcliangc at 308 K. 'Intcmicdiatc ligand exchange in mixturcs of 4 : 1 and 3 : 1 complcxcs at

308 K. 'At 199 K; frcc-bound ligand cxchangc is slow at this temperature but fast

at 308 K.

Solutions in which SPR3/Zn(SbF,), > 4 (R = Ph, o-tol, or Cy) are readily shown by reduced temperature "P nmr spectroscopy to contain Zn(SPR3),", with, presumably, a tetrahedral ZnS, kernel. Phosphorus-31 nrnr data for these complexes are included in Table 2; the values of AS, are similar to those found for the related cadmium complexes ( 1 , 2). Each of the zinc complexes, like Zn(dppmS,)," (above) is less labile than the corresponding cadmium complex. for free and bound ligand signals are incompletely collapsed at 308 K for the zinc complexes, but completely exchange-averaged for the cadmium complexes ( 1 , 2). When SPR,/Zn is reduced below 4, the pale yellow colour of excess SPR, in SO2 disappears and the free ligand line in the reduced temperature "P nmr spectra is no longer seen. Instead, in each case a second signal attributable to bound SPRz is evident. From the variation of resonance intensity as a function of L/M it is clear that Zn(SPR,)," is formed. The "P nmr spectra of the 1 : 3 complexes are outlined in Table 2; again they resemble those of their cadmium analogs. As has been noted for the corresponding cadmium complexes (2), the extent of solvent or anion coordination in these M(SPR,),?' species is not known, so it is unclear whether they contain the expectedly planar MS, core. When SPR,/Zn is reduced below three, an additional signal was observed for R = Cy; this had intensity that varied as expected for Zn(SPCy,)?" and a tentative assignment has been made ac- cordingly (Table 2). (No evidence for Cd(SPCyz)2" was found in earlier work (2).) Similarly, two additional signals were observed for R = o-tol, with an order of appearance and intensity variation suggesting the formation of first Zn(SP(o- tol),)?" and then Zn(SP(o-tol),)". No additional signals were observed for R = Ph. However, we cannot preclude the possi-

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I)E,\N A N D CARSON

TABLE 3 . "P nrnr spcctl.al parameters of some zinc - phosphinc sclcniclc corliplcxcs, z~ ( s~PR, ) , , " . . in liq~rid SO2 at 209 K

11 in S I i S I C I ' J ( ' ~~ -"SC)" A ' J ( ' ~ P - " s ~ ) ~ ScPR," z~(SCPR,),," (ppm) (pprn) (Hz) (Hz)

ScPPh? 4 I.' 29.5 -3.7 582 -7 1 SCPPII, 3' 31.6 -1.5 537 - 1 16 ScP(o-tol)> 4 /..s 30.0 3.0 587 -12 ScP(o-tol), 3 '-I' 28.1 1.1 530 - 89 ScP(o-tol).\ 2 ( ? ) " 30.2 3.2 -508 --I21 ScPCy, 4 I., 61.1 - 1 . 2 55 I - 26 ScPCy, 3".' 64.0 1.7 501 -73 SePCy? 2" 65.1 2 .8 474 - 103 clppmSc2/2' 4 / 27.8 5 .0 574' -112

"o-to1 = o-C,,H,Me; Cy = (.-C,,H,,; tlppmSc, = I'li~P(Sc)CH~P(Sc)l'li~. "Mcasurcd relative to external OP(0Mc); in (CD,)ICO; 6,,1,,,,,, .,,,,,,, = 611,130.,,,,,, - 1.7 ppn:

positive chcmical shifts arc to higher frequency than the rcf'crcncc: estimalcd el-rol. in mcasurcmcnt k 0 . 1 ppm or Icss.

'XI! = G,,(cclrnplcx) - Gl,(frce ligand). "Estimated crror 2 2 Hz, except ~ h c r e 110tcd. "AJ = J(complcx) - J(free ligand). 'Slow excliangc with cxccss frec Iigand at the tcmpclxture of measurement but fast cxch;ingc

at 308 K . 'Fast ligand cxch;~ngc betwcen 4 : I ;uicl 3: 1 complcxcs at 308 K . "Fast ligzind exchange bctwecn 3 : 1 and 2: 1 coiiiplcxcs at 308 K . 'Intcrmcdiatc cxcliangc between 4 : 1 and 3 : 1 complexes at 308 K . 'At I94 K . " 5 Hz.

bility that a 1 : 2 coniplex is formed in this case but gives a Mc

signal coincident with that of the 1 : 3 complex, as was found [Z~(((S)PII,PCH,)~CCH~PP~,(S))~]~~~ for Cd(SP(o- t01)~)~ 3 2 ' (2). of time-averaged C2 syninietry, and therefore we assign

The 209 K "P nnir spectrum of an SO? solution in which ~ ~ ( ~ ~ i ~ ~ d ~ ~ ) , ? t [lie bis(bidentate) structure, on lowering the t r i~hosS, /Zn = 1 showed an AMX spectrum which was as- temperature, slight changes in chemical occur but the signed straightforw:~rdly and is characterized by the parameters change is the sp l i t t ing of. the least shielded resonance given in Table 4 . This pattern is very similar to that observed into two intense colllponents, similar but nlore exten- for Cd(tripliosS3)' ( 1). in which case it was interpreted in sive i n the resonances of the bound - p p h , ( ~ ) groups terms of the monomeric structure I (with a rigid conformation has been found for ~ d ( ~ ~ i ~ ~ d ~ , ) , ? and attributed to destruction at reduced temperature causing inequivalence of the two of (he C , synlll,etry by confornlational effects ( 1 ) . l n the -P(E)Ph? groups) or dimeric structure 11, a prejudice being spectrum of the complex the resonances of the

bound groups are readily apparent because of the ""/"I Cd-

C E 3 ' ~ satellites ( I ) . The "P nnir spectrum of Zn(tripodS,),'~'

PE-M, (Table 4 ) is assigned by analogy with that of Cd(tripodS?)?"

Compleses with phosl,hitze selerzicles

I I1 Coordination is easier to show unanibiguously for phosphine selenides than for phosphine sulfides because for the selenides

expressed for I. The same interpretation can clearly be made it leads not only to a coniplexation shift Ah,) normally, but also here. At 209 K , mixtures in which L/M > 1 give broad "P nmr to a reduction in the magnitude of the 'J(3rP-77Se) satellite resonances indicating ligand exchange at an intermediate rate splitting (from 77Se, 7.58% natural abundance, spin I = 112) between the species present. (Although the conlparative broad- (e.g. refs. 1, 2 , 28-33). ness of the ninr signals made assignment inlpossible, the spec- In the system Zn(SbF6)?-dppniSe, in SOz. the complex tra seem more con~plicated than expected for a simple mixture Zn(dppmSe,)," is readily detected by reduced temperature 3 r P of Zn( t r iph~sS , ) '~ and excess triphosS3.) In contrast, a fast nmr of solutions in which L/M > 2. Details of the spectrum of exchange averaged AXI spectrum is found under the same this presumably tetrahedral complex are given in Table 3; both conditions for cadmium (1). Ahp and ArJ(3'P-77Se) are very similar to those found for

Tripods3, like triphosS,, is a potentially tridentate ligand. Cd(dppn~Se , )~? ' ( 1). The major difference between the zinc and However, the ligand has been shown to behave in a bidentate cadmium coniplexes is in their lability on the nnir timescale: manner in Cd(tripodS3)?" ( 1 ) and similar behaviour is found whereas separate "P nmr signals from zn(dppmSe2)??+ and free using zinc as an acceptor here. Only a 1 : 2 species, dppmSe2 can be observed at 194 K , only an exchange-averaged ~ n ( t r i ~ o d S ~ ) , " , could be identified with certainty in spectrum is observed at this temperature for Cd(dppmSe,)," - Zn(SbF6),-tripods, mixtures using "P nmr. At 308 K this dppmSe, mixtures ( I ) . At 308 K rapid exchange of free and complex, which, in contrast to Cd(tripodS,),"', shows no nmr- bound ligand occurs for Zn(dppniSe,)~"-dppniSe2 mixtures; detectable exchange with free ligand, has a 3 r P nmr spectrum the behaviour at intermediate temperatures is approximately the (Table 4) comprised of three equally intense lines. This is just same as for Zn(dppmS,)," -dppmS, mixtures (see above). the spectrum expected for Complex formation between Zn(SbF,)? and representative

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1804 CAN J . CtIEbI V O L . 01. 1083

TABLE 4. "P nmr spectral p:lrameters of Z n ( t r i p h o s ~ , j 2 ' and Zn(tripoclEl)2" ( E = S or S t ) in licluitl S O ? at 209 K"

61,' AS,,'' I ' J ("P-~~SC)I ' A~J("P-~'sc) ' J ( P P ) ' Cornplcx Phosphorus I' (ppm) (ppm) (Hz) (Hz) ( H z )

Zn(triphosS1)' ' A" 60 .3 8 . 7 'J(AB) = 77 B ' 49.5 5 .6 'J(AC) = 6 8 C ' 45 .5 I . 6 "J(BC) = 0

Zn(ti.iphosSelj2' A" 49.5 6 . 1 I 'J(AB) = 23 B ' 42.1 6.7 I ' J (AC) = 6 6 C i 34.6 -0 .8 -535 --I33 "J(BC) = 0

Zn(tripodS1)22-. " A' 3 0 . 8 -2 .7

B' 32.25 -1.2 'J(PP) 1 32.3, - 1 . 1 (not obs.) C ' 30 .8 -2.7

Z ~ i ( t r i p o d S e ~ ) ~ ~ + ' A "' 19.9 -2 .2 67 2

B "' 18.25 -3.8 540 - 120 'J(PP) 8 . -3.6 546 -114

C"' 16.3 -5.8 5 5 0 2 5 + I 2 ) ( n o t o bs.1 - 110

"TripI~osE, = PhP(E)((CH?),P(E)PIl?)?: tripudE; = McC(CH,P(E)Ph,)>. "Resonances arc I>~bcllc.d as for thc corresponding cndnlium co~llplexcs ( I ). - ' Measured ~rclativc to cxtcl-nal OP(OMc), in (CD,),CO; 8,,,,,,,,,,,;,,,,, - 6,,,,,(,,,,,,, - 1.7 ppm: positive che~~lical shifts arc to higllcr

t'rcquency than tllc I-efcrcncc: cstimotctl error in rneasul-cmcnt 2 0 . I ppm or less. "A61, = 61.(co~l~plcx) - G,,(frce ligand). ' Estinlatcd crror + 2 Hz except tvl~crc noted othcrrvisc. ' AJ = J(cornplcx) - J(frec ligand). 'Estimated crror ? I Hz. "Terminal phospl~orus atom. 'Non-tcrminal phosphorus atom. 'Coultl not bc obscl-vcd with certainty. "Th spectrum consists of tl~rcc resonances at 308 K . ' ~ t 3 0 8 K , 6,,(A6,.) = 31.0(-2.3) . 33.1 (-0.2). and 31.5 ppm(- 1.8 pp~n) , for P,.,. PI,, and Prrcspcctivcly; by analogy with results

for Cd[(SPPli2CH,),McCH2PPh2S]?2* ( I ) P., is assigned to thc unbound ~ P S group.

"'At 308 K . 8,.(A6,,) and 'J(P-Sc) arc 20.0 ( - 1.9) and 702, 18.9 (-3.01, and -545, and 17.0 ppm (-4.9 ppm) and -550 H z for

P,,, PI,, z~nd PC. respectively: escliange with cxrcss frcc ligand is slow at both 209 and 308 K: P, is assigned to the unbound > P S ~

group.

~nonophosphine selenides, IZ,PSe, is indicated visually by blanching of the yellow colour of the ligancl-SO2 solutions (due to R,PSe. SOI (28)). At recluced temperature, "P nlnr spectra attributable to the complexes Zn(SePR,)," (R = Ph, o-tol, or Cy) can be observed; details of the spectra are given in Table 3. At 209 K intern~olecular ligand exchange between the 1 : 4 complexes and the corresponding free R,PSe is slow on the nmr timescale but the rate of exchange becomes rapid by 308 K. In a comparison of the "P nmr spectra of zn(SeP~,) ," (Table 3) and Cd(SePR,)," ( 1 , 2) the most striking similarity is in the values of ' ~ ( " P - ~ ~ s e ) (and hence A J ( " P - ~ ~ S ~ ) ) which are identical within experimental error.

As R,PSe/Zn (R = Ph, Cy, or o-tol) is reduced in the appropriate solutions, the con~plexes Zn(SePR,)," are formed; the "P nmr spectra of these species (Table 3) show sufficient similarity to those of their cadnlium analogs (2) to support these assignments. When R = o-to1 or Cy, entities of even lower ligation number are formed when L/M 2 2. The "P nmr spectra of these (Table 3) have smaller 77Se satellite splittings than the corresponding 1 : 3 conlplexes, and, in addition, the value of ' ~ ( " P - ~ ~ s e ) found when R = o-to1 is close to that observed for Cd(SeP(o-tol),)?" (504 Hz (2)). Hence it is probable that the conlplexes formed are Zn(SePR,)?" (R = o-to1 or Cy). It seems certain that Zn(SePPh,)," is not formed because its smaller 17se satellite splitting should have been evident even if there was no significant "P nmr chemical shift difference between the 1 : 3 and 1 : 2 complexes.

When tr ipho~Se,/Zn(SbF~)~ = 1 , a 1 : 1 complex is formed

giving, at 209 K. a slow-exchange "P nmr spectrum of the AMX type, an easily recognizable and interpretable pattern; the spectral parameters are given in Table 4. However, in many attempts we could not produce Zn(triphosSe3)" as cleanly as Zn(triphosS,)" (see above): the nmr spectruln invariably con- tained other lines varying ,in intensity from attempt to attempt. We can offer no simple explanation for this behaviour, but because of it, and because of overlap with the AMX centre band. not all of the 77Se satellites of the spectrum of Zn(triphosSe,)" could be observed. In con~parison with Cd(triphosSe,)' ' , which undergoes rapid intern~olecular ligand exchange with free triphosse, at all temperatures ( I ) , the zinc con~plex undergoes slower ligand exchange. As for the corresponding trisulfide (see above), broad " 'P nmr lines are found for Zn(triphosSe,)" -triphosSe, mixtures at 209 K. Either of structures I and I1 is consistent with the slow-exchange spectrum of Zn(triphosSe,)".

A 1 : 2 complex, Zn(tripodSe,)z", is formed with Zn" and tripodse, in SOz. At 308 K the "P nmr spectrum of this complex cons,ists of three equally intense resonances and is not noticeably changed in the presence of excess tripodse,. The least shielded resonance (P, in Table 4) has a "Se satellite splitting larger than that of uncomplexed tripodse;, while the other two resonances have smaller values of ' J ( " P - ~ ~ S ~ ) than the free ligand. Clearly only two of the three PSe groups of the ligand are coordinated, and Zn(trip~dSe,)~" ' , like Zn(tripodS3)zz+ (see above), should be formulated as a bis- (bidentate) con~plex of time-averaged Cz symmetry. At re-

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a phosphorus-31 nuclear magnetic resonance spectroscopic study of complexes of zinc with some...

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