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Rhodium trichloride - promoted dimerization of a bidentate olefinic tertiary phosphine to a tridentate olefinic ditertiary phosphine: Additions to metal atom and to ligand and hydrogen abstractions from the ligand in derived complexes of rhodium and iridium

Journal of Organometallic Chemistry
Publication Date
DOI: 10.1016/s0022-328x(00)92878-x


Abstract o-Styryldiphenylphosphine[( o-vinylphenyl)diphenylphosphine], o-CH 2CHC 6H 4PPh 2 (sp) is dimerized by rhodium(III) chloride in refluxing 2-methoxyethanol to give a rhodium(I) complex RhCl(1-bdpb) (IV) containing the tridentate chelate olefinic ligand 1,3-bis[( o-diphenylphosphino)phenyl]- trans-1-but́ene, o-Ph 2PC 6H 4CHCHCH(CH 3)C 6H 4PPh 2- o (1-bdpb) (VI). VI is liberated from IV by reaction with sodium cyanide. IV and its iridium(I) analogue VII exist as mixtures of isomers which have different conformations of the chelate ligand. The isomers of IV interconvert rapidly on the NMR time scale in solution above 122°C with an estimated free energy of activation ΔG≠ (122°) of 20.5 kcal/mol; in the case of VII, the process is slow on the NMR time scale even at 122° (ΔG≠ > 20.5 kcal/mol). The five-coordinate carbonyl complexes MCl(CO)(l-bdpb) (M=Rh, VIII: M=Ir, IX) react with hydrogen chloride to give chelate 2-butyls MCl 2(CO){ o-Ph 2PC 6H 4CH 2CHCH(CH 3)-C 6H 4PPh 2- o} (M=Rh, XIV; M=Ir; XV), the addition being reversible in the case of rhodium. In the presence of triphenylphosphine, IV adds hydrogen chloride to give a chlorine-bridged dimer containing a chelate 1-butyl unit i.e. [ RhCl 2{ o-Ph 2PC 6H 4CHCH 2(CH 3)C 6H 4PPh 2- o}] (XVI). In the absence of auxiliary ligands, VII undergoes irreversible oxidative addition at the metal atom with chlorine and hydrogen chloride, and reversible oxidative addition with hydrogen, to give octahedral, chelate olefin complexes of iridium(III), IrCl 3(1-bdpb) (XII), IrHCl 2(1-bdpb) (XVII) and IrH 2Cl(l-bdpb) (XVIII) respectively; each isomer of VII gives rise to one corresponding isomer in the case of XII and to two corresponding isomers in the cases of XVII and XVIII. IV reacts with chlorine to give RhCl 3(1-bdpb)(XI) and with hydrogen chloride to give a mixture of XI and XVI. XI loses hydrogen chloride irreversibly in solution to form a pseudo-octahedral, chelate n 3-allyl RhCl 2{ o-Ph 2PC 6H 4CHCHC (CH 3)C 6H 4PPh 2- o} (XIII) in which the phosphorus atoms are mutually trans. Although five-coordinate cations [M(CO) 2(1-bdpb)] + (M=RH, XX; M=Ir, XXI), can be isolated as fluoroborate salts, analogous ethylene complexes cannot be obtained; in the case of iridium, the tertiary CH bond of coordinated 1-bdpb oxidatively adds to the metal atom to give a cationic, pseudo-octahedral n 3-allyl hydrido-ethylene iridium(III) complex, [IrH(C 2H 4){ o-Ph 2PC 6H 4CCH-C(CH 3)-C 6H 4PPh 2- o}]BF 4 (XXII). There is also 1H NMR spectroscopic evidence for a minor by-product formed by loss of two hydrogen atoms from 1-bdpb viz. [Ir(C 2H 4){ o-Ph 2PC 6H 4CHCHC(CH 2)C 6H 4PPh 2- o}] BF 4 (XXIII). The reactions of IV and VII are compared with those of similar complexes containing o-Ph 2PC 6CHCHC 6H 4PPh 2- o (bdpps), and the mechanism of dimerization of sp is shown to be analogous to that of the rhodium(III) chloride-catalyzed dimerization of ethylene to 1-butene.

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