Synthesis, Structure, and Reactivity of η²-N₂-Aryldiazoalkane Titanium Complexes:  Cleavage of the N−N Bond

Abstract

A series of η2-N2-titanium aryldiazoalkane complexes Cp*2Ti(N2CHAr) (5−10), where Ar is a para-substituted aryl group, have been prepared by addition of aryldiazoalkanes to Cp*2Ti(C2H4) (4). Unlike most diazoalkane complexes, they release dinitrogen thermally to give transient carbene complexes which may be trapped with styrene to form the titanacyclobutane complexes Cp*2Ti(CHArCHPhCH2) (11−15). The kinetics of these reactions in toluene-d 8 at 78.0 °C have been examined by 1H NMR spectroscopy. A Hammett analysis (ρ = − 0.26) indicated that the reaction is relatively insensitive to para-substituents on the aromatic ring of the diazoalkane ligand, but application of the E- and C-based dual parameter substituent constant analysis suggests that this may be due to almost exactly compensating covalent and electrostatic contributions of each substituent to the reaction rate. The stability of the aryldiazoalkane complexes at temperatures below 75 °C allows their reactivity to be explored without competitive N2 loss. The addition of tBuNC results in a coordination change of the diazoalkane fragment from η2 to η1 to give Cp*2Ti(η1-N2CHPh)(tBuNC) (16), as shown by 15N NMR chemical shifts and N−H coupling constants. The bound tBuNC ligand exchanges with free tBuNC in solution, as established by an EXSY experiment. Trineopentylaluminum coordinates to the terminal nitrogen atom on the diazoalkane fragment to form Cp*2TiN(AlNp3)N(C(H)C6H4Me) (17), as determined by X-ray crystallography. Silanes (HSiR3; R3 = PhH2, Ph2H) add across the Ti−N bond of Cp*2Ti(N2C(H)C6H4Me) to give (E)-Cp*2Ti(H)(N(SiR3)(NC(H)C6H4Me) ((E)-19, (E)-20), the kinetic product and (Z)-Cp*2Ti(H)(N(SiR3)(NC(H)C6H4Me) ((Z)-19, (Z)-20), the thermodynamic product. Diazoalkane adduct Cp*2Ti(N2C(H)C6H4Me) undergoes N−N bond cleavage when treated with CO to form an alkylideneimido isocyanato complex Cp*2Ti(NCO)NC(H)C6H4Me) (21).

Reactions of Group 4 Metallocene Complexes with Mono‐ and Diphenylacetonitrile: Formation of Unusual Four‐ and Six‐Membered Metallacycles

“…In contrast, the second ligand in 5 is an imine species (N1C1 1.232(3), C1C2 1.521(4) Å; N1‐C1‐C2 125.5(3), C1‐C2‐C3 114.2(2), C1‐C2‐C9 109.7(2), Zr1‐N1‐C1 164.6(2)°), which is comparable with the molecular structure of the known zirconocene complex [Cp 2 ClZr(NCHPh)]14 (NC 1.259(7) Å; Zr‐N‐C 170.5(5)°). A titanocene complex with such an imine ligand was also described (NC 1.258(6), CC 1.487(6) Å) 15. Several examples with similar imine ligands are known in the literature for elements such as niobium,16 aluminium,17 iron18 and samarium 19…”

“…A titanocene complex with such an imine ligand was also described (N À C 1.258(6), C À C 1.487 (6) ). [15] Several examples with similar imine ligands are known in the literature for elements such as niobium, [16] aluminium, [17] iron [18] and samarium. [19] In regard to a possible formation pathway, we considered complex 4 to be an intermediate of the reaction from 1 to 5.…”

Synthesis, Bonding and Reactivity of a Terminal Titanium Alkylidene Hydrazido Compound

“…Treatment of [Cp 2 Ti(CO) 2 ] with diethyl diazomalonate (DEDM) formed 1 (Figure 1) containing a κ 3 N , N , O DEDM ligand 6c–e. Andersen and Bergman also employed oxidative routes from [Cp* 2 Ti(η‐C 2 H 4 )] and N 2 C(H)R to form [Cp* 2 Ti{η 2 ‐NNCHR}] (R=SiMe 3 ( 2 a ) or aryl ( 2 b )),6a, s and Chirik et al. prepared [Cp′′ 2 Ti(NNCPh 2 )] ( 3 , Cp′′=1,3‐C 5 H 3 (SiMe 3 ) 2 ) from [(Cp′′ 2 Ti) 2 (μ‐N 2 )] and N 2 CPh 2 in a similar manner 6j.…”

Titanium: Organometallic Chemistry

“…The bound t-BuN≡C ligand exchanges with free t-BuN≡C in solution. 44 Addition of (trimethylsilyl)diazomethane to Cp * 2 Ti(η 2 -C 2 H 4 ) gives the η 2 -N 2 -diazoalkane complex Cp * 2 Ti(N 2 CH SiMe 3 ). Cp * 2 Ti(N 2 CHSiMe 3 ) loses N 2 in solution under mild conditions to give the fulvene complex Cp * (η 6 -C 5 Me 4 CH 2 )TiCH 2 SiMe 3 .…”

“…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.…”