NEW MULTIPLY-BONDED DIMETAL COMPOUNDS CONTAINING BRIDGING 1,3,4,6,7,8-HEXAHYDRO-2H-PYRIMIDO[1,2-A] PYRIMIDINATO GROUPS .1. THE V-2(4-2(4+) AND MO-2(4+) COMPOUNDS AND SOME SALTS OF THE PROTONATED LIGAND(), CR)

The reactions of Lihpp with vanadium(II) chloride, chromium(II) chlori de and tetrakis(trifluoroacetato)dimolybdenum produce the dinuclear te trabridged compounds V-2(hpp)(4), 1, Cr-2(hpp)(4), 2, and Mo-2(hpp)(4) , 3. Compound 1 crystallizes as red blocks in the space group P (1) ov er bar with unit cell dimensions, a = 8.489(2), b = 9.709(2), c = 9.83 5(2) Angstrom, alpha = 89.98(3), beta = 73.04(3) and gamma = 79.29(3)d egrees. This compound contains the shortest known vanadium to vanadium bond, 1.932(1) Angstrom. Compound 2 crystallizes as orange blocks in the space group P (1) over bar with unit cell dimensions, a = 8.488(2) , b = 9.687(2), c = 9.747(2) Angstrom, alpha = 90.89(3), beta = 100.86 (3) and gamma = 106.42(3)degrees. This compound contains a 'supershort ' chromium to chromium bond, 1.8517(7) Angstrom. Compound 3 crystalliz es as red blocks in the space group P (1) over bar with unit cell dime nsions, a = 8.455(2), b = 9.702(2), c = 10.094(2), alpha = 88.84(3), b eta = 72.01(3) and gamma = 79.89(3)degrees and has a short molybdenum to molybdenum bond distance of 2.067(1). Both 2 and 3 have M-M bonds d istances shorter than most analogous compounds containing nitrogen don or atom bridges. The basicity of Hhpp is also evidenced by the formati on of the cation [H(2)hpp](+) upon reaction with trifluoroacetic acid and acetic acid. [H(2)hpp][O2CCF3], 4, crystallizes as colorless needl es in the space group P2(1)/c with cell dimensions, a = 7.431(2), b = 13.243(2), c = 11.741(2), beta = 96.50(3)degrees.[H(2)hpp][O2CCH3], 5, crystallizes as colorless needles in the space group P2(1)/n with cel l dimensions, a = 7.888(2), b = 11.182(2), c = 11.902(2), beta = 91.91 (3)degrees. (C) 1997 Elsevier Science Ltd.