REACTION OF 1,3-BUTADIENE AND ALLENE WITH A DIOSMACYCLOBUTANE

The reaction of the diosmacyclobutane 3 with butadiene gives as a kinetic product the 1,2 adduct Os-2(CO)(8)[mu-CH2CH(CH=CH2)] (4); the thermodynamic product is an allyl acyl dinuclear complex Os-2(CO)(8)(mu-C(O)CH2-eta(3)-CH2CHCH2) (6), derived from 4 by CO insertion. Photolysis of Os-3(CO)(12) in the presence of butadiene gives 6, Os-2(CO)(7)(mu-CH2-eta(3)-CH2CHCH2) (7), and (butadiene)Os(CO)(3) (8). The structure of 7 has been confirmed by X-ray crystallography: orthorhombic, space group P2(1)2(1)2(1), a = 6.928(2) Angstrom, b = 9.473(2) Angstrom, c = 20.683(4) Angstrom, V = 1357.4(6) Angstrom(3), and Z = 4. The reaction of Na-2[Os-2(CO)(8)] with 3,4-dichloro-1-butene or cis-1,4-dichloro-2-butene gave 7 as the principal product. Neither 4 nor 6 rearranged to 7 under thermal conditions, and attempts to carbonylate 7 to 4 or 6 failed at pressures of up to 120 psig. The reaction of 3 with allene gives as a kinetic product the 1,2 adduct Os-2(CO)(8)[mu-CH2C(=CH2)] (9); the thermodynamic product is Os-2(CO)(8)(mu-eta(3)-CH2CCH2) (10). Photolysis of Os-3(CO)(12) in the presence of allene gives 9, 10, and (allene)Os(CO)(4) (11). Allene is bound more tightly than butadiene to the Os-2(CO)(8) unit. The exclusive formation of 1,2 adducts from both butadiene and allene is explained by the fact that substitution in the diosmacyclobutane system occurs via an intermediate 12 with the olefin coordinated to only one osmium atom.