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+), Cr-2(4+) and Mo-2(4+) compounds and some salts of the protonated ligand

摘要

The reactions of Lihpp with vanadium(II) chloride, chromium(II) chloride and tetrakis(trifluoroacetato)dimolybdenum produce the dinuclear tetrabridged 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) over bar with unit cell dimensions, a = 8.489(2), b = 9.709(2), c = 9.835(2) Angstrom, alpha = 89.98(3), beta = 73.04(3) and gamma = 79.29(3)degrees. 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 crystallizes as red blocks in the space group P (1) over bar with unit cell dimensions, a = 8.455(2), b = 9.702(2), c = 10.094(2), alpha = 88.84(3), beta = 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 distances shorter than most analogous compounds containing nitrogen donor atom bridges. The basicity of Hhpp is also evidenced by the formation of the cation [H(2)hpp](+) upon reaction with trifluoroacetic acid and acetic acid. [H(2)hpp][O2CCF3], 4, crystallizes as colorless needles 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) with cell dimensions, a = 7.888(2), b = 11.182(2), c = 11.902(2), beta = 91.91(3)degrees. (C) 1997 Elsevier Science Ltd. [References: 17]