CONTRASTING BEHAVIORS OF PHOSPHORUS AND ARSENIC IN A POLYCYCLIC FRAMEWORK FAVORING PNICTOGEN SQUARE PYRAMIDALITY

The preparations of the novel polycyclic compounds ZPn(OCH2)2CHCHCH2O(CH2OH) and ZPn(OCH2)2C(CH2)xCCH2O-(CH2OH) (Z = W(CO)5, Mn(CO)4Br, Fe(CO)4, CpFe(CO)2+, CpCoI2, Ni(CO)3, Pn = P, x = 1−4; Z = lone pair, Pn = As, x = 2, 3) and also ZP(OCH2)2CHCH2CH2O (Z = W(CO)5, CpFe(CO)2+, Ni(CO)3) are reported. The phosphorus compounds possessing a pendant alcohol group displayed no tendency to coordinate the alcoholic oxygen from 223 to 350 K, even under deprotonation conditions. This was also true where Z = lone pair, O, S, Se, and Ph3C+. Also reported are the preparations of As(OCH2)2CHCHCH2O(CH2OH) and As(OCH2)2C(CH2),CCH2O(CH2OH) (x = 2, 3). The first and second (x = 2) of these compounds are fluxional on the 1H and 13C NMR time scales, presumably owing to the larger size of the pnictogen. A mechanism for the fluxionality, which involves a square-pyramidal transition state, is discussed. The molecular structures of CpCoI2L (L = P(OCH2)3CMe and P(OCH2)2C(CH2)3CCH2O(CH2OH)) determined by X-ray means are presented. The former was found to exhibit a monocline space group P2/n with a = 9.474 (2) Å, b = 8.346 (3) Å, c = 19.416 (5) Å, Z = 4, and β = 102.81 (2)°. The latter eompound was found to exhibit a monoclinic space group P2/c with a = 7.758 (3) Å, b = 19.327 (4) Å, c = 11.958 (2) Å, Z = 4, and β = 97.28 (2)°. The Co-P distances in these complexes are 2.140 (1) and 2.140 (3) Å, respectively. © 1990, American Chemical Society. All rights reserved.