Stchedroff, Marc; (1999) Studies on ruthenium and osmium clusters containing chiral phosphorus and nitrogen compounds. Doctoral thesis (Ph.D.), University College London.

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Abstract

This thesis describes the synthesis, structure (based on IR, MS, NMR and XRD methods) and reactions of novel triosmium and triruthenium carbonyl clusters containing diphosphine and monophosphine ligands, several of which are chiral. Fluxional behaviour (where this is accessible) has been studied, where appropriate aided by 13CO enrichment. The ligand (R)-2,2'-bis(diphenylphosphino)-l,l'-binaphthyl (BINAP) reacts with [Ru3(CO)12] in the presence of trimethylamine-N-oxide (Me3NO) to form [Ru3(OH)2(CO)8(?-BINAP)], rather than the expected product [Ru3(CO)10(BINAP)]. Direct thermal reaction of [Ru3(CO)12] with BINAP leads to an orthometallated product [Ru3(?-H)(CO)9(?3-BINAP-H)]. The cluster [Ru3(OH)2CO)8(?-BINAP)] notably contains the first example of the important ligand BINAP bridging two metal centres and exhibits restricted rotation of two of the four phenyl groups which are graphitically aligned with the naphthyl rings (VT NMR studies). This behaviour appears to be characteristic of the bridging rather than the chelating BINAP ligand. The ligand BINAP reacts with [Os3(CO)12] to give [Os3(CO)11(BINAP)], [OS3(CO)10(BINAP)] and [Os3(?-H)(CO)8(BINAP-H)]. The product [Os3(CO)11(BINAP)] exhibits dynamic exchange of two conformers (dynamic 31P NMR evidence). X-ray structures are reported for [Os3(CO)11(BINAP)] and [Os3(?-H)(CO)8(BINAP-H)]. The 4-tolyl analogue of BINAP (tolBINAP) reacts with [Os3(?-H)2(CO)10] to give [Os3(?-H)2(CO)8(?-tolBINAP)] which was compared with the corresponding 1,2-bis(diphenylphosphino)ethane (dppe), bis(diphenylphosphino)methane (dppm) and related complexes. The X-ray structures of [Os3(?-H)2(CO)8(?-tolBINAP)] and [Os3(?-H)2(CO)8(?-dppm)] are compared in the context of the chain length of the diphosphine ligand. (R)(+)-4-pyridylethanol reacts with [Ru3(CO)10(MeCN)2] and [Os3(CO)10(MeCN)2] to give the products [M3(?-H)(?-C5H3NCHMeOH)(CO)10] (M = Ru or Os) formed by the orthometallation of the pyridine ring. For comparative purposes the known pyridine analogue has been reprepared. The chiral pyridine leads to a diastereomeric mixture which was separated by HPLC and analysed by NMR methods which demonstrate a rigid non-dynamic co-ordination of the organic ligand. An analogous reaction with (S)(-)-nicotine has also been studied and separation by HPLC of the two positional isomers and the diastereomers of each positional isomer achieved. All six chiral clusters prepared have been analysed by CD spectroscopy to establish their relative configurations and the determination of the X-ray structure of one isomer of [Os3(?-H)(CO)10(C5H3NCHMeOH)] has allowed their absolute stereochemistry to be determined. The reactivities of the metal hydride in [Os3(?-H)2(CO)8(?-tolBINAP)] has been compared with that of the parent dihydride [Os3(?-H)2(CO)10]. In particular the ability of unsaturated molecules to add and then insert reversibly into the Os-H bonds has been assessed by the exchange of the hydride ligands with materials such as styrene-dg by isotope labelling methods. A novel means of determming the chemical shifts of 187Os in trinuclear osmium clusters via 1Jh-Os and 1Jp-Os has been developed and tested on a series of compounds at high resolution. These methods enable detection of the least sensitive spin 1/2 nucleus in sample sizes of 50 mg in reasonable experimental times of less than one hour on relatively standard equipment. Significant chemical shift differences have been observed. These methods have only previously been attempted with mononuclear species.

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