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Synthesis and characterization of trinuclear metal clusters containing benzynechromium tricarbonylh Zhang, Hongli

Abstract

The work described in this thesis is directed towards the synthesis of metal cluster derivatives of benzynechromium tricarbonyls. To this end a number of phosphino- and arsinobenzenechromium tricarbonyl ligands such as ER2C6H5Cr(C0)3 (ER2 = PEt2,AsMe2, PPri2, PBut2) and ER[C6H5Cr(C0)3]2 (ER = AsPh, PEt, PBut) have beensynthesized. The structure of PPri2C6H5Cr(C0)3 was determined by means of an X-ray crystallographic study. The reactions of the phosphino- and arsinobenzenechromium tricarbonyl ligands with the trinuclear metal clusters Ru3(C0)12 and 0s3(C0)12 have been investigated. Twenty mono-, di- and trisubstituted complexes were prepared and characterized by using spectroscopic and microanalytical techniques. These are the first examples of metal clusters containing the C6H5Cr(C0)3 group to be synthesized. The structures of four of the substituted complexes were determined by X-ray crystallographic studies. The thermolytic reactions of some ligand substituted triruthenium and triosmium clusters were investigated with the object of preparing the metal clusters containing benzynechromium tricarbonyl. The pyrolytic products were isolated and characterized bys pectroscopic and X-ray crystallographic methods. Several novel benzyne chromiumtricarbonyl complexes were successfully prepared and structurally characterized. The complex Ru3(C0)9[C6H4Cr(C0)3][p,3-C6H5Cr(C0)3] consists of an open Ru3 triangle capped on one face by a g3-phosphinidene moiety and on the other by an unsymmetrically bound benzynechromium tricarbonyl moiety. This is the first example of an aryne to show such unsymmetrical bonding to a Ru3 system. The X-ray crystallographic analysis forRu3(C0)8[C6H4Cr(C0)3][43-PBut] reveals a novel type of benzyne structure, which contains a closed Ru3 framework with a symmetrical benzynechromium tricarbonyl moiety and a phosphinidene ligand on opposite sides. The complex Ru3(C0)8[11-H][C6H4Cr-(C0)3][p,-AsMe2] consists of a closed ruthenium triangle with an arsinido group, a bridginghydride and an unsymmetrically bridging benzynechromium tricarbonyl moiety. This is the first example of an aryne to show unsymmetrical bonding to a closed metal triangle system. One unexpected feature of these three complexes is the presence of Cr-Ru bonding. TheCr-Ru bond distances range from 2.920(1) to 3.097(1) A. These are the first examples of complexes which contain Cr-Ru bonds to be characterized by X-ray diffraction analysis. The first dinuclear metal complex of benzynechromium tricarbonyl Ru2(C0)6[A-1-1][C6H4Cr(C0)3][11.-AsMe2] was also characterized. In addition, two new benzyne complexes, which are of known structural types, were isolated and characterized. Some pyrolytic products other than aryne complexes were isolated and characterized. The complexes H20s3(C0)8L[PPr1C6H4Cr(C0)3] (L = CO, PPri2C6H5Cr-(C0)3) were derived via ortho-metallation of a C-H bond of an 16-bound C6H5 moiety and reductive elimination of a propene molecule. It is interesting to note that the complex 0s3(C0)8(PPhC6H4)[PPh2C6H5Cr(C0)3] is electron deficient. This is the first example of electron unsaturation found in a structure of this type.The investigation of the thermal reactions of the complexes containing benzenechromium tricarbonyls during this work allows some conclusions to be drawn. Phenylchromium tricarbonyl and phenyl groups in triruthenium or triostnium clusters undergo C-H cleavage and C-P cleavage. The isopropyl group undergoes facile 13 C-Hactivation and subsequent C-P activation, while methyl and tertbutyl groups remain intact. It appears that the ease of P-C cleavage follows the order: P-C(Me, But) > P-C(Pri) > P-C(Ph) > P-C(C6H5Cr(C0)3). Comparisons of the thermal reactions of ruthenium and osmium clusters confirm that the latter are generally more thermally stable.

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