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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.

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).

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