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Palladium-Catalyzed Coupling of Ethynylated p-Carborane Derivatives: Synthesis and Structural Characterization of
Wei Jiang1, David E. Harwell, Mark D. Mortimer
1Department of Chemistry and Biochemistry, University of California at Los Angeles, 405 Hilgard Avenue, Los Angeles, California 90095-1569.
Abstract:
Methodology leading to a new class of rodlike p-carborane derivatives is described, involving the palladium-catalyzed coupling of B-iodinated p-carboranes with terminal alkynes. The products of these reactions contain an alkyne substituent at a boron vertex of the p-carborane cage. Reaction of closo-2-I-1,12-C(2)B(10)H(11) (1) with closo-2-(C&tbd1;CH)-1,12-C(2)B(10)H(11) (3) in the presence of pyrrolidine and catalytic quantities of bis(triphenylphosphine)palladium dichloride and cupric iodide yields 1,2-(closo-1',12'-C(2)B(10)H(11)-2'-yl)(2) acetylene (4). Oxidative coupling of 3 in the presence of cupric chloride in piperidine affords 1,4-(closo-1',12'-C(2)B(10)H(11)-2'-yl)(2)-1,3-butadiyne (5). Reaction of 2 molar equiv. of closo-2,9-I(2)-1,12-C(2)B(10)H(10) (6) withcloso-2,9-(C&tbd1;CH)(2)-1,12-C(2)B(10)H(10) (7) in the presence of pyrrolidine and catalytic quantities of bis(triphenylphosphine)palladium dichloride and cupric iodide yields closo-2,9-(closo-2'-I-9'-C&tbd1;C-1',12'-C(2)B(10)H(10))(2)-1,12-C(2)B(10)H(10) (8), a rigid, iodine-terminated carborod trimer in which the p-carborane cages are linked at the 2 and 9 B-vertices by alkyne (C&tbd1;C) bridges. The molecular structures of 5 and the previously described closo-2,9-(C&tbd1;CSiMe(3))(2)-1,12-C(2)B(10)H(10) (9) have been determined by X-ray crystallography. Crystallographic data are as follows: for 5, monoclinic, space group P2/a, a = 12.352(6) Å, b = 14.169 (6) Å, c = 12.384(5) Å, beta = 109.69(2) degrees, V = 2041 Å(3), Z = 4, R = 0.098, R(w)( )()= 0.135; for 9, monoclinic, space group C2/m, a = 22.111(4) Å, b = 7.565(2) Å, c = 6.943(2) Å, beta = 107.871(8) degrees, V = 1105 Å(3), Z = 2, R = 0.059, R(w)( )()= 0.090.