Crystal and molecular structures of pentacarbonyltriphenylphosphinechromium(0) and pentacarbonyl(triphenyl phosphite)chromium(0)

Abstract

Scheme I b' a'(diphos)Ir(CH3) and for (C8H12)[(C6H5)(CH3)2P]2Ir(CH3) are entirely consonant with the mechanism suggested by Shapley and Osborn (see Scheme I) in which there are successive "pseudorotations" about Pt, R, and P2. For equilibration of vinyls 1 and 2 to occur, the reaction must proceed from ground state a, through the high-energy intermediates b and b', back to ground state a'. In the high-energy inter-mediate, a methyl group occupies an equatorial position and the two phosphine groups occupy an equatorial and an axial position. Since ground state a is of higher energy for the diphos compound, due to extra strain associated with a small equatorial P-Ir-P' angle, the diphos compound is expected (as observed) to undergo the intramolecular interconversion a -* a' at a greater rate than the analogous bis-(monodentate)phosphine complex in which the P-Ir-P' angle is not strained by chelation and is closer to the ideal equatorial value of 120°.Further information on these systems is expected to be obtained from current X-ray structural analyses on the species (C8H12)[( C6Hs)2P(CH2)nP(C6H5)2]Ir(CH3) in which n has values other than 2. (The case with n = 2, of course, is covered by the present article.) Registry No. (C8H12)(diphos)Ir(CH3), 36974-34-2. Acknowledgments. S. A. B. gratefully acknowledges the receipt of an NSF predoctoral fellowship. This work was generously supported by the National Science Foundation through Grants GP-26293 and GP-33018 (to M. R. C.).

μ-[Tricarbonyl(1,2,3-triphenyltriphosphane-P 2)nickel(0)-P 1,P 3]-bis[pentacarbonylmolybdenum(0)]

“…The P-Mo and P-Ni bond lengths are normal. The Mo(CO) 5 residues deviate significantly from local C 4 symmetry, as was also found for (CO)sCrPPh a (Plastas, Stewart & Grim, 1973). In both cases this can reasonably be attributed to the lower symmetry of the ligand.…”

Transition-metal complexes of organoaluminum phosphides. Synthesis, characterization, and crystal and molecular structure of Cr(CO)5(PPh2Al)(CH2SiMe3)2.NMe3

“…15 The equatorial Cr-CO linkages in the The geometry about the tetrahedrally-coordinated phosphorus atom is decidedly irregular: the Cr-P-Al angle is increased to 124.64(4)0, the two Cr-P-C angles are inequlvalent [Cr-P-C(21) a115.00(11)0 and Cr-P-C(1l) *105.99(11)0], the Al-P-C angles are close to equivalent CAl-P-C(11) =104.00(11)0 and A1-P-C(21) = 103.40 (11) The aluminum-alkyl distances (Al:CH 2 SiI~e 3 ) are A1-C(la) -1.963 (4) There was no apparent change in the phenyl region of the spectrum to suggest that the phosphorous was complexing the chromium. 2 8 After 9.5 h the reaction mixture had lightened considerably in color and the spectrum showed that a significant amount of product had formed.…”

The structures of dicarbonyl[1–4a(10a)-η-phenanthrene](triethylphosphine)chromium(0) and dicarbonyl[1–4a(8a)-η-naphthalene](triphenyl phosphite)chromium(0)

“…Triethylphosphine is more basic than triphenyl phosphite but the latter is expected to be a better n-acceptor than triethylphosphine because of the electronegative O atoms attached to P. Hence the P atom in triphenyl phosphite will tend to have a greater interaction with the metal atom. These differences in behaviour are well observed in the structures of pentacarbonyl-(triphenylphosphine)chromium and the triphenyl phosphite compound (Plastas, Stewart & Grim, 1973); Cr-P distances are 2.422 and 2.309 A respectively. The further shortening of Cr-P distances in the title compound (NCrP) might be explained by the weaker competitive ligand (naphthalene) compared with carbonyl (Plastas, Stewart & Grim, 1973).…”

“…These differences in behaviour are well observed in the structures of pentacarbonyl-(triphenylphosphine)chromium and the triphenyl phosphite compound (Plastas, Stewart & Grim, 1973); Cr-P distances are 2.422 and 2.309 A respectively. The further shortening of Cr-P distances in the title compound (NCrP) might be explained by the weaker competitive ligand (naphthalene) compared with carbonyl (Plastas, Stewart & Grim, 1973).…”

“…The Cr-P length in the phosphite complex NCrP is 2.217 (1)A, significantly shorter than in the phosphine complex PCrP [2.323 (1)A]; furthermore it is the shortest Cr-P length ever observed. The shortening of Cr-P in NCrP may be explained according to Preston, Stewart, Plastas & Grim (1972), Plastas, Stewart & Grim (1973) and Caldwell, Manojlovid-Muir & Muir (1977) (CMM). Triethylphosphine is more basic than triphenyl phosphite but the latter is expected to be a better n-acceptor than triethylphosphine because of the electronegative O atoms attached to P. Hence the P atom in triphenyl phosphite will tend to have a greater interaction with the metal atom.…”