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Organometallic Complexes of Nickel, Palladium and Platinum

By Richard Wardle

Abstract

We have examined the action of organomercury reagents on complexes of the nickel group in an attempt to find a cleaner route to the organotransition-metal compounds, and in the hope of clarifying the mechanisms involved in these reactions. The reactions between R2Hg (R = Ph or Me) and (R3P)2MCl2(M = Ni, Pd or Pt) yield RHgCl and trans- (R31P)2 MRCl. The reactions with R = Ph proceed more readily than those with R = Me. Reverse reactions between HgCl2 and (R3 1P)2 MR2 produce the same products. R2Hg and the carbonyl complexes (R3 1P) (CO)PtCl2 react to give RHgCl and the previously unknown chlorine-bridged compounds (R3 1P)2 Pt2 (COR)2Cl2. No carbonyl insertion is observed when RLi replaces R2Hg, and Grignard reagents lead to a complex mixture of products. Possible mechanisms of the mercurial reactions are discussed. It seems that the synthetic value of the reactions is small, except for those involving carbonyl insertion. The halogen-bridged binuclear acyl complexes are produced in good yield and can be converted into other derivatives by bridge-splitting reactions using tertiary phosphines or cyclopentadienyl thallium, for example. Till now, very few cyclopentadienyl complexes of palladium or platinum have been reported. We investigated the possibility of using dicyclopentadienyl mercury as an agent to introduce the ligand to complexes of the nickel group. Although we have spectroscopic evidence that (C5H5)2Hg can be so utilised, no organometallic complexes could be isolated from the reaction mixtures due to decomposition of the organomercury by-products. We find, however, that the binuclear halogen-bridged complexes (R3P)2Pd2X4. (R = Et, iPr or Ph; X = Cl, Br or I) react with cyclopentadienyl thallium to produce (pi-C5H5) (R3P)PdX. Yields are poor when analogous platinum complexes are used, but halogen-bridged organoplatinum compounds (R3P)2Pt2R21X2 give good yields of (pi -C5H5) (R3P)PtR1 (R = Et; R1 = Ph or o-tolyl: R = Bu n; R1 = COPh). The complexes (pi-C5H5)(R3P)MX (M = Pd or Pt) react with tertiary phosphines to give either ionic pi-bonded derivatives [(pi -C5H5) (R3P)2M]+X- or unstable d-bonded compounds (R3P)2M(D-C5H5)X, depending on the nature of the solvent and the tertiary phosphine. The same complexes can be produced from (R3P)2MX2and C5H5T1. The nickel complexes (R3P)2iNiX2, on the other hand, react with C5H5-T1 or (C5H5)2Hg to yield (pi -C5H5) (R3P)NiX. The diarsine complex [C6H4(AsEt2)2] Pt (D-C5H5)Cl, produced from [C6H4(AsEt2)2] PtCl2 and C5H5T1, is stable in air to 130. Less stable D-bonded cyclopentadienyl complexes can be prepared from the reactions of (pi-C5H5) (R3P)PtR1 with R3P or CO, or cis-(R3P)(CO)PtCl2 with C5H5T1. The palladium complex (pi -C5H5)(Et3P)PdBr reacts with C5H5T1 to produce the novel derivative (pi-C5H5) ( D-C5H5)Pd(PEt3). Reaction between hydrazine hydrate and (pi-C5H5) (R3P)PdBr (R = Et or iPr) gives the phosphido-bridged complexes [(pi-C5H5 )PdPR2]2. The physical techniques of 1H n. m. r. , i. r. and mass spectroscopy were applied in the characterisation of all the complexes. The platinum derivative C20H20Pt2, first reported by German workers in 1967, has been re-investigated by X-ray analysis. The complex contains a platinum-platinum bond, with a pi-cyclopentadienyl ring bound to each metal atom. The most interesting feature of the structure is the presence of the hitherto unsuspected 5-(5 1-cyclopentadienyl)-cyclopentadiene unit bridging the two metal atoms. Finally, we note that facile pi→ D rearrangement of C5H5 rings is a dominant feature in the chemistry of the cyclopentadienyl complexes of nickel, palladium and platinum, and this interconversion is discussed at several points in the text

Publisher: ProQuest Dissertations & Theses,
Year: 1971
OAI identifier: oai:theses.gla.ac.uk:78560

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