SOLUTION AND SOLID-STATE STRUCTURES OF SALTS OF TRANS-HFE(CO)3PR3- INCLUDING A STUDY OF ALKALI CATION CONTACT ION-PAIRING
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Site-specific contact ion pairing interactions have been examined by v(CO) IR band analysis for Et4N+, K+, Na+ and Li+ salts of trans-HFe(CO)3P- (P = P(OMe)3, P(OEt)3, PMe3, PEt3, PPh2Me, and PPh3). Two major types of contact ion pairs were noted: one involving -Fe-COcation+ interaction and another involving -Fecation+ interaction. A combination of factors, solvent polarity, cation electrostatic potential, cation solvation, and size of the P ligand, determine the ion contact site selection. The indication of -Fecation+ interaction is supportive of a metal-based rather than hydride-based nucleophilicity in hy-dride/halide displacement reactions of HFe(CO)3P- with alkyl halides. The X-ray crystal structure of Et4N+HFe(CO)3PPh3- was determined. It crystallizes in the cubic system, space group Pa3, with cell parameters a = b = c = 17.670 (8) A, V = 5533 (2) A3, and Z = 8. The hydride ligand was not located but indicated to be trans to the PPh3 in a distorted trigonal-bipyramidal coordination geometry. The equatorial CO groups are bent away from the phosphine with a P-Fe-CO angle of 99.5. 1986, American Chemical Society. All rights reserved.