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Unsaturated ditertiary arsine derivatives of some metal carbonyls Mihichuk, Lynn Michael

Abstract

The meso and racemic forms of the new ditertiary arsine, cis-2,3-bis(methylphenylarsino)-1,1,1,k,khexafluorobut-2-ene (L-L)', were prepared "by the reaction of hexafluorobutyne-2 with 1,2-dimethyl-l,2-diphenyldiarsine in hexafluoroacetone. The two diastereomers were isolated and reacted with iron pentacarbonyl affording (L-L)' Fe(CO)₃ and (L-L) Fe₂(C0)₆. Two of the three possible geometric isomers of the latter were obtained and their properties allowed assignment of the configuration of the starting ligands. Minor amounts of the symmetric and asymmetric forms of Fe₂(CO)₆[As(CH₃)(C₆H₅)]₂ were also obtained through loss of fluorocarbon. The complexes Fe₂(CO)₆[E(R₁)(R₂)]₂ (E = As, P; R₁ = R₂ = CH₃; R₁ = CH₃, R₂ = C₆H₅) were prepared and studied by ¹H and ¹³C nmr spectroscopy. Variable temperature ¹H nmr studies indicate the hexacarbonyl complexes are fluxional with respect to the [Fe-E]₂ cluster. Activation parameters were calculated for the motion and possible mechanisms are discussed. The ¹³C nmr spectra of the carbonyl groups at 25° and -70° suggest an independent intramolecular scrambling of the carbonyl groups about the iron atom. Reactions of (L-L)' and the related ditertiary arsine ligand, cis-2,3-bis(dimethylarsino)-1,1,1,h,b,4-hexafluorobut-2-ene (L-L), with the Group VI metal hexacarbonyls gave the chelate complexes (L-L)' M(CO)₄ and (L-L)M(CO)₄. The (L-L)M-(CO)₄ complexes were irradiated with the 450W lamp in the presence of excess (L-L), giving four different types of complexes: fac-(L-L)[sup b](L-L)[sup m]M(CO)₃ and fac-(L-L)[sup b](L-L)[sup m][sup trans]M(CO)₃ (where b and m denote bidentate and monodentate ligand respectively), cis-(L-L)₂M(CO)₂ and trans-(L-L)₂M(CO)₂. The seven-coordinate complexes (L-L)' M(CO)₃X₂ and (L-L)-M(CO)₃X₂ (M = Mo, W; X = Br, I) were prepared and characterized and ¹H nmr spectra at 25° and -70° suggest the complexes are nonrigid. Similarly ¹H nmr studies indicate the seven-coordinate (L-L)LMo(CO)₂ Br₂ complexes are also nonrigid at 25° and -70°. The (L-L)L₂Mo(CO)Br₂ complexes (L is a monodentate phosphite or phosphine) are rigid at 25° and nonrigid at higher temperatures. Activation parameters were calculated for the motion of two of the complexes. Finally, two novel Group VII metal carbonyl complexes of (L-L) of formula C₁₆H₁₈As₃F₅O₆Mn₂ and C₁₁H₈AsF₆O₅Re are described. The former contains a fluorinated n-allyl group bonded to one manganese atom and the latter a CH₂O fragment σ-bonded to rhenium.

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