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Titanium Complexes with Tripodal Amido Ligands: Building Blocks for Stable Bimetallic Coordination Compounds Containing Highly Polar Metal-Metal Bonds** Stefan Friedrich, H a r a l d Memniler , Lutz H . Gade.* Wan-Sheung Li. Mary McPartlin

The spectroscopic data of the moisture-sensitive, red, crys- talline compound (Table 1 ) are in accordance with the structure depicted in Figure 1. Reaction of the complex lC6"l or 2 with

Table I . Selected spectrowopic data. NMR spectra recorded at 200.13 MHz (IH). 50.32 MHz ("C). 77.78 MHz ("Si). and 81.03 MHz ("P) in C,,D,,. Correct ele- mental analyses were obtained for :ill compounds.

Focusing the chemical reactivity at an early transition metal center upon a single "activated" site while effectively shielding the remaining coordination sphere is an underlying motivation of the recent interest in the development of polydentate amido lig- ands.['] A notable example is the reactivity of a series of complex- es containing the silylated tren ligand (tren = tris(2-aminoethy1)- amine) of the type [N{CH,CH,NSiRMe,),MX,] (R = Me. tBu; M = Ti, V, Cr, Mn. Fe. Ta; X = CI, P R ; I I = 0,1,2) report- ed by Schrock et al.['] The anticipated stabilization of a high- valent early transition metal shielded, and thus kinetically stabi- lized, by a polyfunctional ligand appeared to us to provide the key to a general strategy for the synthesis of thermally stable dinuclear complexes containing highly polar unsupported metal -metal bonds. Despite the activities in the chemistry of early -late heterobimetallics there are still but a few stable species of this kind,[31 and their different sets of ligands have hampered a systematic comparative study of their structure and reactivi- ty.14] This led us to develop new tripodal arnides['] (type A) which leave a greater coordination arc at the reactive center than the tren derivatives (Fig. thus potentially facilitating M --MI bond formation. These complexes indeed satisfied the expectations.

x x

A B Fig. I . Titanium-containing building blocks of type A and B for the 5ynthesis of stable heterobimetallic complexes with unsupported metal -metal bonds.

We have now extended this approach to the synthesis of a new class of titanium amido halides (type B) and report the synthesis of one member. Z.[']

The amido titanium bromide 2 is readily obtained by reaction of the trilithiated amino-functionalized trisilylmethane with [TiBr,(thf),] [Eq. (a)].

[HC(SiMeZN(Li)C,H,CH,),l [HC(SiMe,NC,H,CH,),TiBr] (a)

L

[*I Dr L. H. Gade, S Friedrich. H. Memniler lnstitut fur Anorganische Chemie der UniversitHt Am Htihland, D-97074 Wurzhurp (FRG) Telefax: Int code + (931)8884605 W.-S. LI. Prof. M McPartlin School of Chemistry. Unibersity of North London Hollow>iy Road. GB-London N7 XDB (UK)

[**I Thi5 v m r k was supported by the Fonds der Chemischen Industrie (L. H. G.). the Deutsche Forschungsgemeinschaft (L. H. G.. S. F.) and the Scientific and Engineering Rescarch Council (SERC) (M. McP.). We thank Prof. H. Werner foi- his support. We are iilso grateful to Wdcker Chemie AG and Degussd AG for gifts of' basic chemicals.

2 : ' H NMR: S = - 0 28 ( 5 . HC(Si.. . I 3 ) . 0.37 (s, Si(CH,),). 2.07 (5. 4-CH3C,H,). 6.98 (d. 3J1111 = 8.2 HL. H?,,,). 7.10 (d. H3,,,): "C N M R : d = 3.8 ( S I ( C H ~ ) ~ ) , 9.9 (HC(Si. ..Ii). 20.8 i4-CH,C,H4). 123.1. 130.1. 133.4. 148 1 (C1. C4. C3. C1 tolyl): 2 9 S ~ NMR. S = 6.5

3. IH NMR: (5 = 0.41 (5. Si(CH,),). 0.70 is. CH,-C). 3 10 (s. CH,N). 4.59 (s. C-H5): ' "C NMR: 6 = 2.2 (Si(CH3),), 26.7 (CH,-C).49.5 (CH,-C), 60.5 (CHIN), 84.4 (C5H5). 216.6 (CO): 29Si NMR: d = 2.5: IR(toluene): r(C0) = l968(s). 19 16(s) 4- ' H NMR: 6 = 0.40 ( S . Si(CH,),). 0.72 i s . CH,-C), 3.14 (s . CH,N). 4.99 (s.

87.2 (C,H,). 205.6 (CO): '9Si NMR: d =1.9; IR(n-hexane). r ( C 0 ) =1988(s). 1932(s) 5 : ' H N M R : d = 0.46 (s. Si(CH,),). 0.85 (s, CH,-C). 3.35, (5. CH,N). 6.96-7.09. 7.51-7.61 (m. phenyl). "C N M R . 6 = 1 . 3 (Si(CH3)J. 26.4 (CH,-C). 50.2 (CH,- C ) . 61.5 (CH,N). 128.7. 130.1, 133.3 (d, 'Jp, =12.5 H L ) . 135.5 (d, 'J,,<= 39.7 HL) (C?. C4, C?. C1 phenyl). 206.6 ( C O , 'JPc not resolved); "Si NMR: 6 = 7.6: " P N M R : 6 = 56.0; IR(i?-hexane): r(C0) =1930(vs)

c ~ H ~ ) : "c N M R : (5 = 2.3 ( S ~ ( C H J J , 26.5 (cH,-c). 50.3 (cH~-c), 60.6 (cH,N).

6: ' H NMR: 6 = - 0 7X ( 5 . HC(Si.. . ) 3 ) . 0.33 (s. Si(CH,),). 2.21 (s, 4-CH,C6H,). 3.55 is . CIH,) 7.24 (d. 'JI,,, = 8.2 Hz. H2,,,). 7.56 (d. H3,,,j: "C NMR: 6 = 4.0 (Si(CH3):). 6.7 (HC(Si.. .I,). 21.0 (4-CH3C,H,), 85.3 (C,H,). 126.4, 130.3. 132.2. 15O.X (C2. C4. C3. CI tolyl). 213.2 (CO), "Si NMR d = 2.0; IR(henzene): v(COj = 3975(s). 1928(s) 7 : 'H NMR: IS = - 0.68 (s. HC(Si.. .)?). 0.36 ( s . Si(CH,),). 2.20 (s, 4-CW3C,H,).

(Si(CHJ2). 7 1 (HCiSi . . 1 , ) . 20.9 (4-CH3C,H,). 87.6 (C,H,), 126.1, 130.0. 132 2. 149.5 (C2. C4. C3. C1 tolyl). 202.8 (CO). '?3 NMR: 6 = 2 . 6 ; IR(KBr): r(CO1 = 1990(s). 193?(s) 8 : 'H NMR: 6 = - 0.53 (s. HC(Si.. . ) 3 ) . 0.43 (s. Si(CH,),), 2.28 (s, 4-CH3C,H,). 6.69-6.99 (m. phenyl). 7.19 (d, ,JHW = 8.0 H7. H2,,,). 7 61 (d, H3,,,): 13C NMR: d = 4.2 (Si(CHJ2). 8.6 (HC(Si. ..),). 21.1 (4-CH,C,H4). 125.7. 129.4, 132.0. 150.5 (C?, C4, C3. Cl tolyl). 129.3. 129.8. 133.4 (d, *Jpr =12.5 Hz). 134.4 (d. 'J,,< = 40.0 H z ) ( C ~ . C ~ . C ~ . Cl.phenyl).205.1 (d, 'JPc = 16.4 H7.CO): 29Si NMR: d = 3.8. "P NMR: 6 = 56.7: IR(henzene). v(C0) = 2003(w), 1938(vs)

4.07 i s . C,H,). 7.23 (d, 'J , , , , = 8.2 HZ. H2,,,). 7 52 (d, H3J: "C N M R . 6 = 4.0

carbonyl metallate derivatives according to Scheme 1 leads to the coupled heterobimetallic, dinuclear complexes 3-5 and 6-8, respectively. The Ti-Fe complexes, 3 and 6 are the first com- pounds with an unsupported Ti-Fe bond that are stable in solution at ambient temperatures and chemically fairly robust towards attack by weak nucleophiles unless activated thermally or photochemicalIy.[*l

The existence of Ti-M bonds in 3-8 was initially established by IR spectroscopy. The vco bands of the dimers are shifted to higher wavenumbers relative to those of the alkali metal salts of the anions,[', 91 as would be expected for metal-metal bonded structures (Table 1 ) . The absence of vco absorptions attributable to bridging carbonyl or isocarbonyl ligands supports the struc- tural arrangements shown in Scheme 1. Free rotation about the Ti - -M bonds is inferred from the effective threefold symmetry of the titanium-amide moiety observed in the NMR spectra. Cool- ing solutions of 3, 4, 6 and 7 in [DJtoluene 190 K leads to a broadening of the resonances assigned to the amido ligand; how- ever, it proved impossible to reach the low temperature limit.

Single crystal X-ray structure analyses of 3 and 4['01 have established that while the compounds differ significantly with regard to their packing in the crystal and thus space group symmetry, their molecular structures are very similar (Fig. 2). The central structural unit is the free Ti-M bond (M = Fe, Ru), which is effectively shielded by the tripodal amido ligand at the Ti center as well as the set of ligands coordinated to the late

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[H3CC( CH,NSiMe3)3TiBrl

1

M = F e 3 5

Ru 4

Y Y

I I

M = F e 6 8

Ru 7 Scheme 1 . Condensation of 1 (type A ) and 2 (type B) with late transition mztal carbonylates.

transition metal. The average Ti-Fe distance of 2.433 A in the structure of 3 and the Ti-Ru distance of 2.527(1) A in that of 4 are significantly shorter than the corresponding bond lengths observed in [Cp(CO),MTi(NMe,),] [dJTi-Fe) = 2.568.[4b1 d(Ti-Ru) = 2.663(1) A]r11aJ and [Cp(C0),RuTi(NMe2)(2.6- Me,C,H,Oj,] [d(Ti-Ru) = 2.573(1) A].['1b1 In fact, the Ti-Fe bond length in 3 is the shortest hitherto observed for an unsup- ported transition metal-metal single bond in a a consequence both of the high bond polarity and the low steric hindrance of the two halves of the molecule."3J

The essentially linear carbonyl ligands lean markedly towards the Ti atoms [mean Ti-Fe-CO 82.6' (3) ; mean Ti-Ru-CO 80.8- (4)], but the Ti . . . CO distance of about 2.8 A in each compound precludes any "semi-bridging" interaction and indicates that the disposition of these ligands is largely determined by the steric requirements of the bulky cyclopentadienyl group. Repul- sion between this ligand and the large N-bonded Me,% groups at the other side of the Ti- Fe or Ti-Ru bond results in two silyl groups being forced apart (as can be seen in Fig. 2b) , thus breaking the otherwise threefold symmetry of the Ti complex fragment. The polydentate triamido ligand is clearly sufficiently flexible to accommodate these distortions without a significant destabilization of the bimetallic molecule.

In order to establish the basic structural arrangement in the bimetallic complexes derived from 2, an X-ray structure analysis of 7 was carried out (Fig. 3)."" A striking feature is the lamp-

Fig. 2. a) Molecular structure of 3; b) view# along the Fe-Ti axis of 3 Selected mean bond lengths [A] and interbond angles [ ' I for the two independent molecules in the asymmetric unit. Ti-Fe 2 433(5), Fe-C6 1.73(2). Fe-C7 1.68(2),Ti-Nl 1.90(2). Ti-N2 l.XX(2). Ti-N3 l.XY(2); Ti-Fe-CG S1.3(8). Ti-Fc-C7 83.8(8). C6-Fe-C7 96(1), Fe-Ti-N1 114.1(5). Fe-Ti-N2 116.1(5). Fe-Ti-N3 117.3(6). Corresponding bond parameters of 4. which has a very similar molecular structure (hut only one molecule in the asymmetric unit): Ti-Ru 2.527(1). Ru-C6 1.840(9). Ru-C7 1.835(9). Ti-Nl 1.907(5). Ti-N2 1.905(6). Ti-N3 1.907(6): Ti-Ru-Ch 7Y.h(3). TiLRtiK7 X l . Y ( 3 ) , Ch-Rii-C7 93.1(4). Ru-Ti-Nl 118.1(2), Ru-Ti-" 115.3(2), Ru-Ti-Ni 113.1(2).

shade arrangement of the tripodal amide in which the tolyl groups are oriented almost orthogonally to the radial planes spanned by the Ti, N. and Si That this orientation of the amido tolyl groups is retained in solution may be inferred from the shift of the signals of the Cp protons in the 'H N M R spectrum of 7 to higher field (6 = 4.07 in comparison to 4.99 in 4). The Ti-Ru bond therefore appears less shielded than in 4. and it may be due to this situation that the metal-metal bond [d(Ti-Ru) = 2.503(4) A] is even shorter than that observed in 4. All other structural features related to the metal-metal bond

IYI

Fig. 3. Molecular structure o f7 in the crystal. Selected bond lengths [A] and inter- bond angles [ ]: Ti-Ru 2.503(4). Ru-C8 l.Sl(2). Ru-C9 l.XO(2). Ti-N1 1.93(1). TI-NZ 1.90(1)< Ti-N3 1.90(1); Ti-Rn-CS 87.8(7). Ti-Ru-CY 88.4(8). C8-Ru-CY 91.2(8). Ru-Ti-N1 113.9(4). Ru-Ti-NZ 112.7(5). Ru-Ti-N3 117.7(5)

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resemble those of 3 and 4. In view of the similarity of the NMR data of 6 and 7 as well as the band-to-band analogy of the IR spectm. an almost identical structure may be assumed for the Fe analogue 6.

The general applicability of the concept of Ti-M bond stabi- lization by use of Ti complex fragments containing polydentate ainido ligands was demonstrated by the synthesis of the Ti -Co species 5 and 8. Stable dinuclear compounds with this structural element have been elusive until re~ent ly”’~ due to their extreme thermal lability. Both 5 and 8 can be readily handled in solution and were found to be sufficiently stable at ambient temperature to enable ;I systematic investigation into their reactivity.”81 In general. type A and B Ti amides therefore appear to “do the trick” i n stabilizing Ti-M (M = late transition metal) hetero- bimetallics.

E.xperiiiwtiu1 Procedure 2: A 7.5 hi solution ofii-butyllithium in hexanes (5.72 mL) was added to a mixture of HC(SiMc,NHC,H,CH,), (2.41 g. 4 72 mmol) [Sb] in pentane (30 niL) and di- ethyl ether ( 2 mLJ. ~ h i c h uiis cooled at -50 C The reaction mixture was subse- quently u;iriiicd and stirred at room temperature for 2 h. The resulting lithium ainide \uspension was then cooled to -50 C, solid [TiBr,(thf),] (2.69 g =

idded. and the reaction mixture warmed to room temperature over 20 h Evaporatioii ofthrsolvciit.exti-action ofthe residue with toluene(20 mL). and liltralion ~ielded ii deep red filtrate. which was concentrated to 10 mL and stored at -40 C to kield 2 ‘is red crystals. Yield: 1.65 g (55%). 3 8: Solid .ilkall carbonyl rnetalate (1 mmol) was added to a solution of 1 or 2 (1 minol. l b r I458 mg. for 2 631 mg) in toluene (30 mL) cooled at -70 C. and the reaction iiiixtiii-c uarmcd to rooin temperature over a period of 20 h . Evaporation of tlic solbcnt. extraction of the residue with pentane (20 mL), and subsequent filtration 4 ieldcd ).cllo\v-orange solutions of the heterobimetallic complexes. Evap- oration 01the solvent yielded the reaction products a s inicrocrystalline solids, which Mere u,ished with cold pentane. isolated yields: 3 59%, 4 68%. 5 48%. 6 61 %. 7 73?b, 8 3Y‘!,,. Single crystals suitablc for X-ray crystaiiography were obtained by slou coolit if of wlutioiis of the compounds in toluene.

Received: Octobcr 13. 1993 [Z 6414 IE] German version: A i i p i . Chciii. 1994. 106. 705

[I] W. M P B Menge. J. G. Verkade. /iiorg. Chon. 1991. 30. 4628: A. A. Naiini, W. M . P. B. Menge. J. G. Verkadc, ihid. 1991. 30. 5009: J. G. Verkade, Acc. C.heii i KP\ 1993. 36. 483.

[2] <’. C Cuinmins. R . R. Schrock. W. M. Da\ia. Orguiioiiieiri//i~,.s 1992. I f , 1452; c‘. C. Cumrnins. J Lee. R. R. Schrock. W. M . Davis. Angrw.. Choin. 1992, 104, 1510: .Iri,cy11. ( h r i i i . / i i r . Ell. h g l . 1992. 31, 1501: C . C . Cummins, R . R. Schrock. W. M . Davis. iM. 1993, 105, 758 and 1993. 33. 756

131 D. W Stephan. C ~ r d . Chrm. REV. 1989. Y j , 41. [4] a) C P Cascy. J Orgunoinet. Chivii. 1990. 1/10, 205 and references therein:

b) W J. Sxtaiii. J. P. Selcgue. OIXuitoiiic.rrri/i[T 1987. 6. 181 2. [S] a ) L H Gade. N. Mahr, J C/wn. SOC. Udtoii Truii5. 1993.489: b) L. H. Gade.

C. Bcchcr. J. bb! Lauher. /nor.q. C ’ h o n 1993. 33, 2308. [6] a ) S. Friedrich. L H. Gade. A. J. Edwards. M. McPartlin. Chein. B w . 1993.

/ ? . 1797: h ) .I Chriir. So(,. Uulron Traii, . 1993. 2x61. [ 7 ] Burger sl al h \ e reported the unsuccesafiil attempt to coordiiiate the in situ

1ithi;ited HC(SiMe,NHMe), to titanium(iv) centers: a ) H. Burger, R. Mellies. cl. J Oi-,quiioiiiet. C/wiii. 1977. 142. 55. We have found that the use of iryl-wbstituted amines of this type lcads to stable titanium complexes:

h) H. Mrmniler. L. H. Gade. J W. Lauher. I ~ O V K . Chrvrr.. submitted. [ X I The o n l y knouii example of a titanium compound of thnt type. Selegur‘s

[Cp(C‘O)l~eTi(NMe,),]. was reported to decompose rapidly in solution at ambient temperature [4b]. Case). et al. reported the synthesis of [CpiZi - (K)I~e(CO)zCp/] (R = C H , . OtBu) and [Cp,Zr(Fc(CO),Cpl,]. The latter I \ only stable in solutioii at temperatures below -20 C : C. P. Caaey. R. E .lordmi. A. I.. Rheingold. J. .Am. Chc,iii. SOL.. 1983, 10.5. 665. O ~ g ~ i i ? o n w r i i / - / I ( , \ 1984. .?. 504.

[9] M. Broohhai-t. W B. Studabaker. R. Husk, ~ V g u i i ~ i i i ~ , / [ i / / i C , \ 1987. 6. 3141. [I01 Crybrala o f3 ruitablc for X-ray studies were difficult to obtain and diffracted

onl) poorlq. This resulted in relatively high standard deviations o n all parame- ters. hut (he iniiin features of the structure are well established. Crystal data of 3 ( ,,H,,N,O,Si,TiFe, monoclinic, spacc group P l , ‘ 1 1 . (I =15.496(3).

F(000) = 2352, R = 0.0699.K, = 0.0709 for 2301 reflcctiuiis with /,‘o(/) > 3.0 corrected for absorption [p(MoKr) = 9.1 cm-’1. Crystal data of‘ 4: C,,H,,N,OISi,TiRu, monoclinic. space group P2,:c. L I =12.Y77(3)./1 =12.084(3).( =18.217(3) A,/) = 91.33(2)‘.M = 600.73. I’=

1. = 29.219(3) A. /i = 104.518(2) . ,M =555.57. I , = 5690 71 A’. =1.297

2855 Y I A I, Z = 4. pcdlUd = 1 397 g c r C 3 . F(000) = 1248. R = 0 0484;R, =

0.0518 for 2903 reilections with lo(/)> 3.0 corrected for absorption [Ir(Mo,,) = 9.0cm-’].

[ I l l a) W. S. Sartain. .I. P. Selegue, ./. h i . Cheni. S O ( . 1985. 107. 5818: h) Or.quiioriri,/ri//ii.s 1989, 8. 21 53.

[I 21 Cambridge Structural Database, Cambridge University. 1993. [13] Whether d,-d, backbonding plays a role in these heterobimetallics a s invoked

for the ligund-bridged Zr- Rh complex [Cp*Zr(p-OCH2Ph,P),RhMe2] [d(Zr- Rh) = 2.444(1) A](G. S. Fcrguson, P. T, Wolcranski. L. Piirkiiiiyi. M . C. Zon- nevyllc. Orjianonw/u//ics 1988, 7. 1967) remains to be investigated in MO cLiIcii-

lations of appropriate model systems. [14] See. for example. F. A. Cotton, Pmg. /iiorg. Chcwi. 1976, 21. I . F. A. Cotton.

J. M. Troup, J. Ain. Chem. Soc 1974. 96, 1233; W. I . Biiiley, D. M Collins, F. A. Cotton. J. Orgunoiiic/. Chem. 1977. 13.5, C53.

1151 Crystal data of 7: C,,H,,N ,O,Si,TiRu. monoclinic. space group 12:c.

l’=7h01.X4A3. L = 8. ocrlLd =1.351 gcm-’. F(000) = 3200. R = 0.0663’ R, = 0.0667 for 1904 reflections with /‘o(/) > 3.0 corrected for absorption [ii(MoKI) = 6.9 cin-’1. Further details ofthe crystal structures :ire available on request froin thc Director of the Cambridge Data Centre. 17 Union Road. Cambridge CB2 1 EZ. UK on quoting the full journal citation.

[I61 A preliminary X-ray structure analysis of the aterically less crowded precursor 2 has revealed a similar arrangement of the tolyl groups [7 b]. \*hich is therefore not to be interpreted as solely a consequence of the steric inter;iction wi th the Ru complex fragment.

[I71 D. Selent. R. Beckhaus, J. Pickardt. Or~jiliiic’”i[,rii//i~,\ 1993. 12. 2857. The only other structurally characterized example o l a compound containing a n unsup- ported Ti-Co bond was reported by G. Schmid. B. Stuttc. R. Boese. Chm. Brr. 1978, I l l . 1239.

[18] I f solutions o f 5 or 8 in benzene ;ire stirred at room teinperaturc over ii period of .stveru/ r i c i j x slow decomposition sets in and generates [ jCo(CO),(PPh,)l,] which precipitates from the solution.

( I = 24.4733). h =15.417(3). c = 20.783(4) A, /< =104.20(2) , :M =772.92.

Direct Metal-Metal Bonds Between High and Low Valent Complex Fragments: The Reaction of Metal Bases with the Metal Acids [Re(NR),j +

and [Mo(NR)J* + ** Jorg Sundermeyer,* Diane Runge, and John S. Field Dedicated to Professor Wolfgang S u n d e r n q w on the occccsion of his 65th hirthduj

The synthesis of heterobimetallic complexes in which a metal center deficient in d-electrons (f block element, metal of the group 4 or 5 ) with a complex fragment rich in d-electrons (typical- ly a metal of group 8) fixed in close proximity is enjoying steadily growing interest. The combination of antipodes of the periodic system (early-late heterobimetallics)[’I holds the promise of co- operative behavior on the part of the metal centers in the activa- tion of smaller molecules,[2’ an increased catalytic activity in the homogeneous phase, or at least an insight into the interaction of immobilized catalysts with oxide support materials.[31 Com- parable synergistic effects could also be achieved by the combi- nation of the same metal, or of two metals close to one another

[*I Dr. J. Sundermeyer. DipLChem. D. R u n g lnstitut fur Anorpanische Chemie der Universitlt Am Hubland D-97074 Wurzhurg (FRG) Telefax. Int. code + (931)888-4605 Prof. J. S. Field Department of Chemistry and Chemical Technology University of Natal P. 0 Box 375. Pietermaritrburg 3200 (South Africa)

[**I Hohervalente Derivate der d-Metall-Siuren, Part 9. This uork was supported by the Deutsche Forschungsgemeinschaft, the Fonds der Chemischen Indus- trie. the South African Foundation for Research Development. and the Uni- veraity of Natal. We would like to thank Prof. Helmut Werner for his support and Dr. Lutr Gade for his expert debates. Part 8 : J. SundermeSer, K . Weber. K. Peters. H. G. von Schnenng. Orgunoinr~tu//ic.s. submitted.