REGIOSPECIFIC LIGAND ADDITION TO THE DONOR-ACCEPTOR COMPOUND RU-2(CO)(6)(BPCD) - SYNTHESES AND X-RAY-DIFFRACTION STRUCTURES OF RU-2(CO)(5)L(BPCD) AND RU-2(CO)(5)L[MU-C=C(PPH2)C(O)CH2C(O)](MU(2)-PPH2) (WHERE L = PME3 AND (BUNC)-BU-T)

Thermal and Me3NO-assisted activation of the donor-acceptor complex Ru -2(CO)(6)(bpcd) (1) [where bpcd = ,5-bis(diphenylphosphino)-4-cyclopen ten-1,3-dione] with PMe3 or (BuNC)-Bu-1 affords the mono-substituted c omplexes Ru-2(CO)(5)L(bpcd), as a result of regiospecific ligand attac k at the diphosphine-substituted ruthenium center. Solution NMR measur ements (H-1 and P-31) reveal that the PMe3 derivative exists as a noni nterconverting mixture of axial (3a) and equatorial (3e) isomers, with the only the equatorial isomer being observed for Ru-2(CO)(5)((BuNC)- Bu-1)(bpcd) (5). Near-UV irradiation of 1 in the presence of added lig and yields Ru2(CO)SL(bpcd), in addition to the known mu(2)-phosphido c omplex Ru-2(CO)(6)[mu-C=C(PPh2)C(O)CH2C(O)](mu(2)-PPh2) (2) and the co rresponding phosphido-substituted complexes Ru-2(CO)(5)L[mu-C=C(PPh2)C (O)CH2C(O)](mu(2)-PPh2) [4 (L = PMe3); 6 (L = (BuNC)-Bu-t)]. As with c ompounds 3a, 3e, and 5, both 4 and 6 exhibit ligand attachment at the diphosphine-substituted ruthenium center. The molecular structures of 3e, 4, 5, and 6 were determined by X-ray crystallography. 3e, as the 1 /2 C6H6 solvate, crystallizes in the monoclinic space group C2/c: a = 40.573(3) Angstrom, b = 10.2663(9) Angstrom, c = 18.347(1) Angstrom, b eta = 95.371(6)degrees, V = 7609(1) Angstrom(3) and Z = 8; 4, crystall izes in the monoclinic space group P2(1)/n: a = 10.8241(8) Angstrom, b = 18.074(1) Angstrom, c = 19.194(1) Angstrom, beta = 96.968(6)degrees , V = 3727.3(5) Angstrom(3), and Z = 4; 5, as the 1/2CH(2)Cl(2) solvat e, crystallizes in the monoclinic space group C2/c: a = 40.955(3) Angs trom, b = 9.7230(6) Angstrom, c = 20.542(1) Angstrom, beta = 106.596(5 )degrees, V = 7839.2(9) Angstrom(3), and Z = 8; 6, as the 1/2C(5)H(12) solvate, crystallizes in the monoclinic space group P2(1)/c: a = 21.7 73(2) Angstrom, b = 10.907(3) Angstrom, c = 18.744(4) Angstrom, beta = 114.68(1)degrees, V = 4045(1) Angstrom(3), and Z = 4. The site occupi ed by the PMe3 and (BuNC)-Bu-1 ligands in these compounds is discussed relative to the steric size/electronic properties of the ancillary li gand and its interaction with the bpcd ligand.