Syntheses and Reactivity of Metal Cluster Complexes with Borylene as a Bridging Ligand

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[Co_2 (CO)_8] reacted with B_2H_4・2PMe_3 to form a borylene complex [Co_7 (CO)_7 (BHPMe_3)] where borylene is stabilized by the phosphine. This is the first example of a borylene bridged dinuclear complex. B-H and B-B bond fission accompanied the reaction. This is in contrast to hitherto known coordination compounds of electron precise boranes such as BH_3・PMe_3 and B_2H_4・2PMe_3 in which B-H or B-P bonding are kept intact. Ultraviolet irradiation of methyl complexes, [CpWMe (CO)_3] and [CpFeMe (CO)_2] which are electron-rich with cylopentadienyl group in the presence of BH_3・PMe_3 liberated methane to form boryl complexes [CpW (BH_2PMe_3) (Co)_3] and [CpFe (BH_2PMe_2)], respectively. These reactions were accompanied by the B-H bond cleavage. Phtochemical reaction of [Cr (CO)_6] in the presence of BH_3・PMe_2CH_2PMe_2・BH_3 gave a five-membered diborane derivative by the dehydrogenation and B-B bond formation, which coordinated two chromium moieties through four Cr-H-B bonds to form [{Cr (CO)_4}_2 (BH_2BH_2PMe_2CH_2PMe_2)]. The structure was analyzed by the X-ray crystallography. This cluster can be regarded as a dimetalatetraborane derivatives. Reaction of [Cp^*RuCl]_4 with BH_3・PMe cleaved a strong B-P bond followed by the Cl atom transfer to give a chlorotrihidroborato complex. This complex is expected to be a versatile starting material for the formation of borylene complex because it has a reactive B-Cl bond.