TITANIUM(II), TITANIUM(III), AND TITANIUM(IV) COMPLEXES SUPPORTED BY BENZAMIDINATE LIGANDS

The synthesis and reactivity of a wide range of titanium benzamidinate s is described. Addition of 0.5 equiv of Me2Mg to the dichloride L2TiC l2 (L = PhC(NSiMe3)(2)) in Et2O yields the chloro-alkyl derivative L2T i(Me)Cl in good yield. The addition of 2 equiv of PhCH2MgCl to the dic hloride affords thermally sensitive L2Ti(CH2Ph)(2) in moderate yield. Likewise, addition of 1 equiv of Me2Mg results in the clean formation of the dimethyl L2TiMe2. The dimethyl reacts with tert-butylamine in r efluxing benzene to form the five-coordinate imido L2TiNCMe3, for whic h crystallographic data is presented. The imido reacts with acetone in C6D6 to form the bridging oxo derivative L2Ti(mu-O)(2)TiL[eta(1)-NC(P h)N(SiMe3)(2)]. Overnight reduction of the dichloride with 1% Na/Hg am algam in tetrahydrofuran (THF) forms the Ti(III) derivative L2TiCl(THF ), which is crystallized from hexanes in moderate yield. Carrying out the analogous reduction in toluene yields the base-free Ti(III) chlori de, L2TiCl, for which crystallographic data is presented. Allowing the reaction (in toluene) to proceed for an additional 48 h results in fu rther reduction and the formation of the end-on bound dinitrogen compl ex (L2Ti)(2)(mu-N-2), which is isolated as dark blue crystals from hex anes in moderate yield. Reduction of L2Ti(Me)Cl with 1% Na/Hg amalgam in THF forms the Ti(III) methyl derivative which is isolated as the fi ve-coordinate THF-free product L2TiMe upon evacuation and crystallizat ion from hexamethyldisiloxane (HMDSO). The related Ti(III) alkyl L2TiC H2SiMe3 is readily prepared by reaction of LiCH2SiMe3 with L2TiCl in t oluene. Carrying out the 1% Na/Hg amalgam reduction of the dichloride in the presence of CO results in the formation of the Ti(III) bridging -ore species (L2Ti)(2)(mu-O), which is isolated in low yield. CO as th e sole oxygen source is confirmed by the use of (CO)-O-18, which yield ed only labeled product. Analogous reduction in the presence of N,N,N' ,N'-tetramethylethylenediamine (TMEDA) results in the C-N bond cleavag e of an amidinate ligand and the cycle metalation of TMEDA. Two produc ts, L2TiNSiMe3 and LTi[eta(2)-Me3SiNC(H)Ph] [eta(3)CH(2)N(Me)CH2CH2NMe 2], are isolated in good yields by fractional crystallization from hex anes. The dinitrogen complex, (L2Ti)(2)(mu-N-2), reacts with pyridine (Py) and 2,6-dimethylphenyl isocyanide (XylylNC) to form base adducts [L2Ti(PY)](2)(mu-N-2) and [L2Ti(CNXylyl)](2)(mu-N-2) without loss of t he dinitrogen ligand. Crystallographic data for the Py adduct is prese nted. Oxidation reactions of (L2Ti)(2)(mu-N-2) with a variety of oxyge n and sulfur sources is reported. Reaction with dry O-2 in the presenc e of pyridine gives the seven-coordinate peroxo complex L2Ti(eta(2)-O- 2)Py. The related reaction with excess S-8 yields the dark-green persu lfido derivative L2Ti(eta(2)-S-2), for which crystallographic data is presented. The persulfido reacts overnight with Hg in toluene solution to give the bimetallic sulfide complex L2Ti(mu-S)(2)TiL[eta(1)-NC(Ph) N(SiMe3)(2)], which is formed following a silyl-group migration. The a nalogous oxygen-containing product is best prepared by the reaction of powdered (L2Ti)(mu-N-2) with dry O-2. In the presence of excess pyrid ine, L2Ti(eta(2)-S-2) reacts with Hg to yield the terminal sulfide L2T i(S)Py. The crystallographically characterized terminal-ore derivative L2Ti(O)OPy is prepared by reaction of (L2Ti)(mu-N-2) with an excess o f pyridine N-oxide in toluene-pyridine.