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Aspects of organometallic chromium nitrosyl chemistry Shaw, Michael J.

Abstract

The behavior of a series of paramagnetic organometallic complexes, CpCr(N0)(L)X, (Cp = 175-05H5; L = phosphine or amine; X = Cl or I) in solutions has been investigated by ESR spectrometry and cyclic voltammetry. The 17-valence electron CpCr(N0)(L)X compounds undergo ligand substitution in donor solvents, S, forming either CpCr(N0)(S)I or [CpCr(N0)(L)(S)]I complexes, depending on the conditions used. The CpCr(N0)(L)X complexes display irreversible reduction behavior in THF/0.1M En-Bu4NFF6. The complexes are moderately difficult to reduce. Interestingly, the reduced species are more substitutionally labile than their odd-electron precursors, in contrast to the usual observed trend where even-electron species are less labile. The kinetics of the substitution of THF for PPh3 on the CpCr(N0)(THF)(I) complex have been investigated by using UV-V is spectroscopy. The unusual 17-valence electron alkyl complexes CpCr(N0)(L)R (R = CH2SiMe3,CH2Ph) have been prepared and studied. Some of these complexes display unprecedented delocalization of the unpaired electron throughout the coordination sphere of the metal as determined by ESR and X-ray crystallography of the CpCr(N0)(PPh3)CH2SiMe3complex. This complex possesses the ability to lose ligands selectively to attain an 18-valence electron configuration. For example, reaction of CpCr(N0)(PPh3)CH2SiMe3 with NO and [INTO]+ results in the formation of the 18-valence electron CpCr(NO)2CH2SiMe3and [CpCr(NO)2PPh3]+ complexes, respectively. Reaction of the CpCr(N0)(PPh3)CH2SiMe3 complex with HSnPh3 yields the first isolable chromium nitrosyl hydride, CpCr(N0)(PPh3)(H)(SnPh3). The solid-state molecular structure of the hydride complex has been established by X-ray methods. The reaction of CpCr(N0)(PPh3)I with Me3SiCH2MgC1 to obtain CpCr(N0)(PPh3)CH2SiMe3 has been studied in some detail by ESR and IR spectrometry. The alkyl complex forms via initial ligand exchange of PPh3 for a solvent molecule, followed by coordination of the nitrosyl oxygen to the organomagnesium reagent. The halide-for-alkyl metathesis step occurs when the thus-formed isonitrosyl complex reacts with another equivalent of the Grignard reagent. Finally, the CpCr(N0)(L)I complexes undergo N-0 bond cleavage when reacted with (mes)MgBr (mes = 2,4,6-C6H2Me3). Further reaction results in the formation of CpCr(N-mes)(mes)(0) and CpCr(N-mes)(mes)I. The latter complex has been structurally characterized by X-ray crystallography. The CpCr(N-mes)(mes)(0) complex reacts with CO to produce (mes)C(0)NH(mes), thus effecting an overall transformation of a coordinated nitrosyl ligand to an organic amide.

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