Crystal structure of (3,3 ',4,4 '-tetramethyl-1,1 '-diphosphaferrocen-2-yl) carboxylic acid and its bis-[W(CO)(5)] complex center dot 0.5C(5)H(12): Conformation of 1,1 '-diphosphaferrocenes

The structures of (3,3',4,4'-tetramethyl-1,1'-diphosphaferrocen-2-yl)carbox ylic acid (I) and its bis-[W(CO)(5)] pentane solvate complex (2) have been determined by X-ray analysis. The compound 1 crystallizes in the monoclinic P2(1)/n space group with Z = 4; a = 7.8404(9), b = 14.9441(16), c = 11.773 0(14) Angstrom, beta = 92.773(10)degrees, V = 1377.8(3) Angstrom(3), and D- calc = 1.553 g cm(-3). The compound 2 crystallizes in the triclinic <P(1)ov er bar> space group with two complex molecules and one pentane molecule in the unit cell. Cell parameters: a = 10.7070(2), b = 12.577(2), c = 13.239(3 ) Angstrom, alpha = 84.00(2), beta = 77.58(1), gamma = 66.06(1)degrees, V = 1591.0(5) Angstrom(3), and D-calc = 2.100 g cm(-3). The fully eclipsed con formation of the phospholyl rings with P ... P secondary bonding of 3.353(1 ) Angstrom is observed in 1 and a partially eclipsed conformation is found in 2. The 10 possible conformations of 1,1'-diphosphaferrocenes were descri bed as the function of conformational parameter theta and observed geometry of the phospholyl rings.(7) We suppose that the earlier conclusions concer ning the destabilizing nature of 1,1'-diphosphaferrocene conformations with a < 100 degrees cannot be considered as general. The mode of W-P coordinat ion, the structural changes of 1 by W(CO)(5) coordination, the structural e ffect of phospholyl rings substitution by the -COOH group, and hydrogen bon ds are analyzed.