STABILIZATION OF LOW-COORDINATED M(CO) BU ILDING-BLOCKS - SYNTHESIS AND REACTIVITY OF ((ETA(5)-C(5)H(4)SIME(3))(2)HF(CCPH)(2))M(CO) (M=NI,CO)

The synthesis and reactivity of the dinuclear compounds (L(2)Hf(C=CPh) (2))M(CO)(L = eta(5)-C(5)H(4)SiMe(3); M = Ni: III; M = Co: V) are desc ribed. The organometallic diyne PhC=C-L(2)Hf-C=CPh (I) reacts with Ni( CO)(4) (II) or Co-2(CO)(8) (IV) to afford in high yields III or V, res pectively. In III and V, both phenylethynyl units are eta(2)-side-on c oordinated to M(CO) building blocks. Along with the paramagnetic compl ex V, compound L(2)Hf(C=CPh) [mu-(eta(2)-C=CPh)Co-2(CO)(6)] (VI) can b e isolated. Reaction of VI with more Co-2(CO)(8) (IV) yields the compo und L(2)Hf[mu-(eta(2)-C=CPh)Co-2(CO)(6)](2) (VII). The reaction of L(2 )M(C=CR)(2) (M = Hf, R = Ph: Ia; M = Ti, R = Ph: Ib; M = Ti, R = SiMe( 3): Ic) with Fe-2(CO)(9) (VIII) yields L(2)M[(eta(2)-C=CR)Fe(CO)(4)](2 ) (M = Hf, R = Ph: IXa; M = Ti, R = Ph: IXb; M = Ti, R = SiMe(3): IXc) . In IX each of the two C=CR groups is eta(2) -side-on coordinated to the 16-electron fragment Fe(CO)(4). When III is treated with P(OR)(3) (R=CH3: Xa; R=(C3H7)-C-i: Xb) carbonyl substitution is observed to for m (L(2)Hf(C=CPh)(2))Ni[P(OR)(3)] (R = CH3: XIa; R =(C3H7)-C-i: XIb). T he identity of all new compounds is confirmed by analytical and spectr oscopic (IR, H-i NMR, C-13 NMR, P-31 NMR, MS) data. Additionally, the structures of I and V were established by X-ray diffraction.