Shinhmar, Mukesh Kumar; (1997) Synthesis and reactions of tertiary phosphines containing heterocyclic substituents with transition metal carbonyl complexes. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis describes an examination of the synthesis and coordination chemistry of tertiary phosphines, PPh2R, containing the 2-substituted heterocyclic substituents R = pyridyl, thienyl and furyl and the 2- and 3- substituted heterocycle, pyrrolyl, based on the dinuclear and trinuclear metal carbonyls, [M2(CO)10] (M = Mn, Re) and [Os3(CO)12], respectively. For each of the ligands, substitution of up to two axial carbonyl ligands in [Mn2(CO)10] and up to two equatorial carbonyl ligands in [Os3(CO)12] occurs, to give simple phosphorus-bound monosubstitution compounds. Analogous compounds are not observed with [Re2(CO)10]. Other simple compounds, formed from the reaction of [Mn2(CO)10] with the furan and pyrrole ligands, include [Mn2(μ-H)(μ-PPh2)(CO)8], which contains a hydride and a diphenyphosphido bridge and a related substitution compound, [Mn2(μ-H)(μ-PPh2){PPh2(2-C4H3X)}(CO)7] (X = O, NH). Compounds involving coordination of the heterocyclic substituent of the ligand, via the heteroatom, the carbon atoms, or both, have also been characterised. The bis and tris pyridylphosphines bridge dimanganese compounds via the phosphorus atom and the nitrogen atoms of two pyridyl units, to yield the related compounds, [Mn2{μ-PR(2-C5H4N)2}(CO)7] (R = Ph, 2-C5H4N). Diphenyl-2-thienylphosphine reacts thermally with [Mn2(CO)10] to give [Mn2(μ-PPh2){μ-η1:η5-(C4H3S)}(CO)6], a complex derived from P-C bond cleavage which contains bridging diphenylphosphido and 2-thienyl units. This latter bridge coordinates to one Mn atom via the 2-carbon atom and to the other Mn atom via all the ring atoms. A related Re compound is formed thermally; it differs in that only the S atom of the cleaved thienyl unit coordinates to the second Re atom. A precursor to this, which does not contain a cleaved thienyl unit, is formed photochemically. The ligand bridges the two Re atoms via the phosphorus and sulfur atoms. Diphenyl-2-pyrrolylphosphine gives a trimanganese compound in which the ligand bridges two of the Mn atoms via the phosphorus and nitrogen atoms and the other Mn atom is coordinated as a tricarbonylmanganese unit to all the atoms of the 2-pyrrolyl unit. [Os3(CO)12] reacts with the ligands to give clusters containing a hydride bridge and a σ,η2-vinyl group, which as expected, exchange between metal centres at a slower rate than their Ru analogues. These clusters have a high thermal stability and only react at a high temperature to give an open trinuclear cluster which contains μ3-heterocyclic and phenylphosphido units on opposite faces of the triangle and which are derived from the loss of benzene. Two forms of this cluster can be visualised for diphenyl-3-pyrrolylphosphine which are not distinguishable by spectroscopic techniques. With diphenyl-2-pyrrolylphosphine a cluster containing the ligand bridging the Os atoms via a P-N bridge and the 2-carbon atom is also formed.

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