THE SUBSTITUTION CHEMISTRY OF MULTIPLY BONDED DITUNGSTEN AND DIRHENIUM COMPLEXES (DINUCLEAR COMPOUNDS, PI-ACCEPTOR LIGANDS, ALKOXIDES, REACTION CLEAVAGE)
Abstract
The doubly bonded ditungsten(IV) alkoxide W(,2)Cl(,4)- ((mu)-OEt)(,2)(EtOH)(,2) has been shown to reductively couple ketones RR'C=O to form a new carbon-carbon bond and produce the ditungsten(V) species W(,2)Cl(,4)((mu)-OEt)(,2) RR'C(O)C(O)RR' (,2), where R = R' = Me or R = Me and R' = Et, which contain two bridging (alpha)-diol ligands. The mechanism of this reaction is believed to proceed via initial displacement of the two EtOH ligands by ketone molecules. Reductive coupling then occurs with the electrons required for this process being supplied by the W-W bonds. The presence of isomers within the crystalline sample has been investigated using ('1)H NMR spectroscopy. The substitution chemistry of multiply bonded dirhenium complexes containing bridging bidentate phosphine ligands has also been explored with regard to their reactions with isocyanides, nitriles and carbon monoxide. The monoisocyanide complexes Re(,2)X(,3)(dppe)(,2)(CNR) ('+) and Re(,2)Cl(,4)(dppm)(,2)(CNR) (X = Cl or Br; R = Me, i-Pr, t-Bu or xylyl), each of which formally contain a Re-Re triple bond, have been isolated and an X-ray crystal structural determination of Re(,2)Cl(,4)(dppm)(,2)(CN-t-Bu) was performed. The structurally characterized species possesses an A-frame-like structure with a terminally bound t-BuNC ligand. The substitution chemistry of the A-frame complexes has been extended to reactions with nitriles, R'CN, to yield Re(,2)Cl(,3)(dppm)(,2)(CNR)(NCR') ('+) and with CO to produce Re(,2)Cl(,3)(dppm)(,2)(CNR)(CO)(,2) ('+). In addition, a complex possessing three isocyanide ligands coordinated to a dirhenium center, Re(,2)Cl(,3)(dppm)(,2)(CNxylyl)(,3) ('+) has been isolated. These dinuclear complexes which contain one, two, or three molecules of a (pi)-acceptor ligand provide information on the reaction steps which precede metal-metal bond cleavage. New dirhenium species containing alkyl-substituted diphosphine ligands have been synthesized and their reactivity toward (pi)-acceptor ligands has also been investigated. All of the new complexes have been fully characterized by electrochemical and spectroscopic techniques.
Degree
Ph.D.
Subject Area
Chemistry
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