Synthesis of an η²-N₂-Titanium Diazoalkane Complex with Both Imido- and Metal Carbene-Like Reactivity Patterns

Abstract

The novel η 2 -N 2 -diazoalkane complex Cp* 2 Ti(N 2 CHSiMe 3 ) (2) has been prepared by addition of (trimethylsilyl)diazomethane to Cp* 2 Ti(C 2 H 4 ) (1). The structure of 2 reveals nearly symmetric Ti-N distances and an N-N distance ∼0.1 Å longer than that of the free diazoalkane. Compound 2 loses dinitrogen in solution under mild conditions to give the fulvene complex Cp*FvTiCH 2 SiMe 3 (4). Thermolysis of 2 in the presence of 1-alkenes yields the trans-R, -disubstituted titanacyclobutane complexes Cp* 2 Ti(CH(SiMe 3 )CH- (9)). The regio-and stereochemistry of the titanacyclobutane complexes was determined by a combination of one-and two-dimensional NMR techniques. The NMR assignment was supported in the case of 8 by an X-ray diffraction study. In addition to confirming the regio-and stereochemistry of the metallacycle, the X-ray structure of 8 shows that unlike most titanacyclobutanes, the metallacycle ring is puckered. A kinetic study of the formation of 7 from 2 and styrene revealed that the reaction is first order in 2 and zero order in styrene. The rate constant for this reaction is identical to that measured for the conversion of 2 to 4. The kinetic study supports a mechanism involving initial rate-determining loss of dinitrogen to form a carbene complex intermediate which undergoes hydrogen transfer from a Cp* methyl to give 4, or in the presence of styrene is trapped to form 7. In addition to its metal carbene-like reactions involving N 2 loss, complex 2 undergoes a variety of transformations in which N 2 is retained in the final product. These include cycloaddition reactions with alkynes and allene, as well as reversible reactions with Lewis bases to form adducts. These transformations, which are similar to reactions of group IV imido complexes, demonstrate the imide-like character of the diazoalkane ligand.

Diazoalkane Reduction for the Synthesis of Uranium Hydrazonido Complexes

“…The resulting structure of complex 4 has a U1-N41 bond length of 2.348(6) Å, indicative of a uranium(IV)-nitrogen(amide) bond. Bergman previously reported analogous reactivity for Cp* 2 Ti(η 2 -N 2 CHSiMe 3 ) [31] with both acetylene and phenylacetylene to produce the corresponding metallacycles. [19,[45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62] This is most likely due to increased s character at the U-C44 bond as a result of multiple bonding at the adjacent carbon-carbon bond (C44-C45).…”

“…Bergman's Cp* 2 Ti(η 2 -N 2 CHSiMe 3 ) [31] displays single bond character between the titanium atom and both Nα and Nβ in the molecular structure. Bergman's Cp* 2 Ti(η 2 -N 2 CHSiMe 3 ) [31] displays single bond character between the titanium atom and both Nα and Nβ in the molecular structure.…”

Titanium: Organometallic Chemistry

“…Thermolysis of Cp * 2 Ti(N 2 CH SiMe 3 ) in the presence of 1-alkenes yields the trans-α, β,-disubstituted titanacyclobutane complexes Cp * 2 Ti(CH (SiMe 3 )CH(R)CH 2 ). 45 The titanocene vinylidene intermediate Cp * 2 Ti(=C=CH 2 ) formed by ethane or methane elimination from titanacyclobutane (4) or Cp * 2 Ti(CH=CH 2 )Me, respectively, reacts with isothiocyanates, RNCS (R = C 6 H 11 , Ph or t-Bu), by a [2 + 2] cycloaddition, to give the titanathietane complexes (8). In all cases, the regioisomer in which the S atom is bonded to Ti is found as the primary product.…”

“…99 Treatment of {η 5 :η 1 -C 5 R 4 SiMe 2 N-t-Bu}TiMe 2 (R = H, Me) with HOCMe 2 CH 2 CH 2 CH=CH 2 gives a mixture of {η 5 -C 5 R 4 SiMe 2 NH-t-Bu}TiMe 2 (OCMe 2 CH 2 CH 2 CH=CH 2 ) and {η 5 :η 1 -C 5 R 4 SiMe 2 N-t-Bu}TiMe(OCMe 2 CH 2 CH 2 CH=CH 2 ). Treatment of a mixture of {η 5 -C 5 R 4 SiMe 2 NH-t-Bu}TiMe 2 (OCMe 2 CH 2 CH 2 CH=CH 2 ) and {η 5 :η 1 -C 5 R 4 SiMe 2 N-t-Bu} TiMe(OCMe 2 CH 2 CH 2 CH=CH 2 ) with B(C 6 F 5 ) 3 3 gives a reactive metallocene cation complex that instantaneously undergoes CH activation at a N-CH 3 group to yield the metallacyclic constrained geometry complex (44) Reduction of (η 5 :η 1 -C 5 Me 4 SiMe 2 NR)TiCl 2 (R = t-Bu, Ph) with BuLi in the presence of various 1,3-dienes gives the unique constrained geometry diene complexes, (η 5 :η 1 -C 5 Me 4 SiMe 2 NR)Ti(diene) complexes (45). The diene coordination mode (π , formally Ti(II), or metallacyclic, formally Ti(IV)) and the activity for olefin polymerization are highly sensitive to the identity of R. 205 Treatment of (η 5 :η 1 -C 5 Me 4 SiMe 2 NR)TiCl 2 (R = t-Bu, CHMe(1-C 10 H 7 )) with butadienemagnesium gives butadiene complexes analogous to (39) in good yield.…”

Organometallic consequences of a redox reaction: Terminal trimethylsilylmethylidene titanium complexes prepared by a one-electron oxidation step

“…In contrast, group 4 transition metal compounds bearing the terminal trimethylsilylmethylidene ligand are even more scant, with the only reported examples (isolable) being the titanium and zirconium complexes (PNP)Ti@CHSiMe 3 (X) (PNP À = N[2-P(CHMe 2 ) 2 -4-methylphenyl] 2 ) [19][20][21][22]; X À = OTf [23], CH 2 SiMe 3 [17]) and [C 5 H 3 (SiMe 2 P i Pr 2 ) 2 ]Zr@CHSiMe 3 (Cl) [24,25], respectively. In most cases, the M = CHSiMe 3 functionality in question must be trapped or generated in situ, to avoid decomposition pathways from occurring [26][27][28][29]. In rare cases however, dimers arise from bridging of the trimethylsilylmethylidene unit [30,31].…”