J. H. G. Frijns

Dichloromethane addition to rhodium-β-diketonate complexes of diphosphines and pyridyl-substituted diphosphines

Abstract In the reactions of the pyridyldiphosphine ligands (C6H5)(C5H4N)P(CH2)n-P(C6H5)(C5H4N) (n = 1, DPyPM; n = 2, DPyPE; n = 3, DPyPP) with (β-diketonate)Rh(COD), only the phosphorus atoms coordinate to rhodium. The DPyPE and DPyPP complexes react with dichloromethane to give eventually pyridyl-ylid complexes [(β-diketonate)Rh(Cl)(CH2NC5H4)(C6H5)P(CH2)nP(C6H5)(C5H4N)]Cl. The (chloro)(chloromethyl) complexes thought to be intermediates can be isolated if aryl-diphosphines (C6H5)2P(CH2)nP(C6H5)2 are used in the reaction. The structure of the pyridyl-ylid complex [(dipivaloylmethanate)Rh(Cl)(CH2DPyPE)]Cl has been determined by X-ray diffraction. The rhodium atom is octahedrally surrounded by the two oxygen atoms of the β-diketonate, one axial chlorine, and one axial phosphorus atom (that bearing the pyridyl-ylid group), and the remaining phosphorus atom and the methylene group in the equatorial positions. The ylidic CN bond is rather long (1.510(4) A).

Mono- and bi-nuclear molybdenum complexes of 2,6-bis(diphenylphosphino)-N-methylaniline

Abstract The new ligand 2,6-bis(diphenylphosphino)- N -methylaniline (LH) has been prepared via repeated o -lithiation of lithium N -methyl- N -phenylcarbamate. Reaction of LH with Mo(CO) 6 gives [ P,N -LH]Mo(CO) 4 ( 1 ) and (with an excess of Mo(CO) 6 ) [μ- P,N : P ′-LH][Mo(CO) 4 ][Mo(CO) 5 ] ( 3 ). Reaction of the anion L − with Mo(CO) 6 initially gives the carbamoyl complex {[ P,C -LC(O)]Mo(CO) 4 } − Li + ( 4 ), but use of an excess of Mo(CO) 6 and extended reaction times results in formation of the binuclear complex {[μ- P,N : P′,N -L][Mo(CO) 4 ] 2 } − Li + ( 5 ). Complex 5 does not react with oxygen, but treatment with halogen sources (CCl 4 , Br 2 , I 2 ) gives [μ- P,N : P′,N -L][μ-X][Mo(CO) 3 ] 2 ( 6 , X = Cl, Br, I) via an intermediate formulated as {[μ- P,N : P′,N -L][Mo(CO) 4 ][Mo(CO) 3 X 2 ]} − Li + ( 7 ). All complexes have been characterized by 13 C and 31 P NMR spectroscopy. The structure of 6 -Br has been confirmed by a single-crystal X-ray diffraction study. The molecule of 6 -Br is of approximate C s symmetry; each molybdenum atom is surrounded by three carbonyl groups, a phosphine, bridging nitrogen and bromine atoms (MoN = 2.18 and MoBr = 2.70 A av.) and the second molybdenum atom (MoMo = 2.987(2) A). The metal-metal distance and electron-counting rules indicate the presence of a single metal-metal bond.

Formation and reactions of bis(phosphino)succinic anhydrides

A route to 2,3-bis(phosphino)succinic anhydrides and related compounds is described. The compounds are formed by reaction of a secondary phosphine with maleic anhydrides which bear a leaving group at the alkenic carbon atom. The reaction of bromomaleic anhydride with diphenylphosphine proceeds via diphenylphosphinomaleic anhydride. An acid-catalysed Michael addition leads to cis-2,3-bis(diphenylphosphino)succinic anhydride, which in turn rearranges to the trans isomer by an acid-catalysed process. The trans isomer was isolated as a hydrobromide. The formation of diphosphines from the corresponding maleic acids and esters has also been observed. A primary phosphine does not lead to a phosphinosuccinic anhydride.Addition of a base to the bis(phosphino)succinic anhydride generally leads to the elimination of the phosphine moiety. However, the anhydride ring can be opened with sodium methoxide and a diphosphine, with both a carboxylic acid and a carboxylate ester moiety, is formed in moderate yield. Two conformers or isomers of this compound are obtained, both of which decarboxylate readily to give methyl 2,3-bis(diphenylphosphino)propanoate.Co-ordination of the diphosphine system to PtII prevents both the elimination of secondary phosphine and the decarboxylation of carboxylic groups.

On the direct metalation of tertiary phenylphosphines

Abstract We have envisaged a route towards ortho-phosphinobenzoic acids via direct ortho-metalation of tertiary phenylphosphines. The direct metalation of tertiary phenylphosphines with BuLi/KOt-Bu or BuLi/TMEDA proves to be an a-selective process. After carbonation mixtures of carboxylic acids are obtained. With BuLi/KOt-Bu/THF the reaction occurs preferably at the meta and para positions. With BuLi/TMEDA/hexane all three possible positions are metalated. Introduction of an auxiliary methoxy group leads to a higher selectivity. Blocking of all meta and para positions with methoxy groups leads to metalation in the ortho position. The rate of metalation at the ortho position is relatively slow. Observed side reactions are: substitution of phenyl groups, α-metalation, and substitution of a methoxy group.