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Dive into the research topics where Howard C. Clark is active.

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Featured researches published by Howard C. Clark.


Journal of Organometallic Chemistry | 1985

Tin-119, phosphorus-31, carbon-13 and proton nuclear magnetic resonance and Mössbauer studies of mono-, di- and tri-organotin(IV) dialkyldithiophosphates

Howard C. Clark; Vimal K. Jain; R. C. Mehrotra; B. P. Singh; G. Srivastava; T. Birchall

Abstract 119 Sn, 31 P, 13 C and 1 H NMR chemical shifts of organotin(IV) dialkyldithiophosphates have been measured in CDCl 3 . The 119 Sn NMR chemical shifts and || 1 J ( 119 SnSn- 13 C)|| and || 2 J ( 119 Sn- 1 H)|| of triorganotin(IV) dialkyldithiophosphates are consistent with tetrahedral, four-coordinated tin, although Mossbauer studies indicate five-coordinated tin in the solid state. The 119 Sn NMR chemical shifts, || 2 J ( 119 Sn- 1 H)|| and Mossbauer parameters of mono- and di-organotin(IV) dialkyldithiophosphates are indicative of weak coordination of the ligands to tin.


Journal of Organometallic Chemistry | 1981

The hydroformylation reaction: catalysis by platinum(II)-tin(II) systems

Howard C. Clark; Julian A. Davies

Abstract The complexes [Pt(ER 3 )(CO)Cl 2 ] (E = P, As; R = aryl, alkyl) are active precursors for the catalytic hydroformylation of olefins in the presence of added tin(II) chloride. The yield of aldehyde may be maximized by systematic parameter variation and is shown to be limited by the degree of steric crowding at the metal centre. Terminal aliphatic monoenes are hydroformylated readily with a high n : iso ratio; hindered internal olefins, cyclic and conjugated aromatic olefins are less readily hydroformylated, but with no competing hydrogenation. The catalyst system is active under mild conditions of temperature and pressure.


Coordination Chemistry Reviews | 1987

Ligand Interactioins in crowded molecules

Howard C. Clark; Mark J. Hampden-Smith

Cas des complexes de grosses phosphines. Interaction dans les complexes cis- et trans-XYPt(PCy 3 ) 2


Journal of Organometallic Chemistry | 1985

Preparation and characterization of mercapto-bridged dinuclear platinum(II) complexes. Catalytic activity of [(PEt3)PtCl(μ-SEt)]2/SnCl2 · 2H2O system in hydrogenation and hydroformylation of styrene

Howard C. Clark; Vimal K. Jain; G.S. Rao

Abstract A series of complexes [(PR 3 )PtX(μ-SR′)] 2 (PR 3 = PEt 3 , PPr 3 n , PBu 3 t or PMe 2 Ph; X=Cl, SnCl 3 , Me, Ph or COPh; R′=Et or Pr i ) and [(P-C)Pt(μ-SR′) 2 (P-C= metalated tri-t-butylphosphine; R′ = Et, Pr n , Pr i Bu n , Bu i ) has been prepared and characterized by elemental analyses, 1 H, 31 P, 13 C and 119 Sn NMR spectroscopy. The stereochemistry of the complexes in solution and the trans influence of the SR′ ligands are discussed. The catalytic activity of the [(PEt 3 )PtCl(μ-SEt)] 2 /SnCl 2 · 2H 2 O system in styrene hydrogenation and hydroformylation has been described.


Journal of Organometallic Chemistry | 1984

Organoplatinum(IV) compounds. II: Preparation and characterization of trimethylplatinum(IV) compounds with chelating nitrogen donor ligands. The crystal and molecular structure of iodotrimethyl[bis(3,5-dimethyl-1-pyrazolyl)methane]platinum(IV)

Howard C. Clark; George Ferguson; Vimal K. Jain; Masood Parvez

Compounds of the types Me3PtX(NN) (where X = Cl, I, OAc, NO3; NN = bis(1-pyrazolyl)methane (pz2CH2), bis(3,5-dimethyl-1-pyrazolyl)methane ((Me2pz)2CH2), or bis(2-pyridyl)methane (py2CH2)), [Me3Pt(NNN)][PF6] (where NNN=tris(1-pyrazolyl)methane (pz3CH), or tris(2-pyridyl)methane (py3CH)), and [Me3Pt((Me2pz)2CH2(py)][PF6] have been prepared and characterized by elemental analyses and 1H and 13C NMR spectroscopy; the structure of Me6PtI[(Me2pz)2CH2] (1) has also been determined by X-ray crystallography. Crystals of 1 are orthorhombic, space group Pcmn with four molecules in a unit cell of dimensions a 11.936(5), b 14.462(4), c 10.138(5) A. The structure was solved by the heavy-atom method and refined by full-matrix least-squares calculations to R = 0.022 for 1719 observed data. The molecule has crystallographic mirror symmetry. The Pt atom has octahedral geometry with one methyl group trans to iodine and two methyl groups trans to the N atoms of the bidentate ligand (PtI 2.843(1), PtN, 2.236(4), PtC 2.077(6) (trans to I) and 2.032(5) A (trans to N)).


Journal of Organometallic Chemistry | 1983

The stereochemistry of organotin(IV) oxinates in solution: TIN-119 nuclear magnetic resonance study of triorganotin(IV) oxinates

Howard C. Clark; Vimal K. Jain; Ian McMahon; R. C. Mehrotra

Abstract Contrary to the previously proposed fluxional trigonal bipyramidal structure for triorganotin(IV) oxinates, the 119 Sn NMR chemical shifts of these compounds are consistent with tetrahedral, 4 coordinate tin. No fluxional processes could be detected in the 1 H and 13 C NMR spectra of Me 3 SnOx down to −90°C.


Journal of Chemical Crystallography | 1982

The structure ofcis-dichloro-bis-(triphenylphosphine)platinum(II); a product in the reaction ofcis-[PtCl2(CO)(PPh3)] with tin (II) chloride

G. K. Anderson; Howard C. Clark; J. A. Davies; George Ferguson; Masood Parvez

The reaction ofcis-[PtCl2(CO)(PPh3)] with two equivalents of SnCl2. 2H2O in acetone solution allows isolation ofcis-[PtCl2(PPh3)2] as the acetone solvate, the crystal structure of which has been determined. Crystals ofcis-[PtCl2(PPh3)2]·C3H6O are monoclinic, space groupP21/c (No. 14) with four formula units in a cell of dimensionsa=10.288(3),b=24.372(5),c= 15.367(3) Å, /gb=98.07(2)°. The structure was solved by the heavy-atom method and refined by full-matrix least-squares calculations to a finalRof 0.033 for 3761 reflections withI>(I). The crystal structure contains discrete well-resolvedcis-PtCl2(PPh3)2 molecules with acetone of solvation filling cavities in the crystal structure. The Pt coordination is slightly distorted square-planar with Pt-Cl 2.333(2) and 2.356(2), Pt-P 2.251(2) and 2.265(2) Å, P-Pt-P 97.8(1), and Cl-Pt-Cl 87.1(1)°.


Journal of Organometallic Chemistry | 1981

Preparation and characterization of some cationic five-coordinate methylplatinum(II)tris(1-pyrazolyl)methane complexes

Howard C. Clark; M. Adediran Mesubi

Abstract Methylplatinum(II) complexes of the type [Pt(CH3)(HCpz3)L]+PF−6 (pz = 1-pyrazolyl; L = CO, H2CCH2, CH3CCC6H5, CF3CCCF3 or CH3O2CC CCO2CH3) have been prepared and characterised by means of elemental analysis, IR and 1H NMR spectroscopy. Their structures have been deduced by comparing their NMR data with those of the analogous hydrotris(1-pyrazolyl)borate complexes. The stereochemical nonrigidity of these complexes is discussed on the basis of their variable temperature NMR spectra. The NMR studies indicate that the fluxionality of the tris(1-pyrazolyl)methane ligand decreases with increasing electron-withdrawing ability of L. The complexes are inert towards insertion of L into the PtCH3 bond.


Inorganica Chimica Acta | 1979

Chemistry of platinum hydrides. Part XXII. Formation of trinuclea cluster complexes from platinum(II) dihydrides containing bulky phosphines

Howard C. Clark; Anil B. Goel; Chun S. Wong

Abstract Carbon monoxide reacts readily under ambient conditions with platinum(II) dihydrides containing bulky phosphines, PtH2(PR3)2 (where PR3 = Cy3P, Pri3P, But2BunP and ButPh2P) i benzene solution displacing hydrogen as well as one phosphine ligand and giving trinuclear cluster complexes cotaining bridging carbonyl groups. These cluster complexes, which can aloso be preprared by the reactions of carbon monoxide with (PR3)2Pt, undergo oxidative addition reactions with iodine, giving tetracoordinated platinum(II) complexes, PtI2(PR3(CO).


Journal of Organometallic Chemistry | 1984

Mixed ligand complexes of platinum(0) containing diphosphines

Howard C. Clark; Pramesh N. Kapoor; Ian McMahon

Abstract The reaction of PtCl2L (L = diphosphine) with the appropriate diphosphine L′ in ethanol followed by reduction with aqueous sodium borohydride leads to either disproportionation to give mixtures of the bis(diphosphine) complexes PtL2 and PtL′2 or to the formation of the mixed ligand complex PtLL′ depending on the diphosphines. Mixed ligand complexes are obtained when L=Ph2P(CH2)2PPh2, L′ = Ph2P(CH2PPh2 cis-Ph2PCH CHPPh2, Ph2P(CH2)2AsPh2, Ph2- P(CH2)4PPh2, o-Ph2PC6H4PPh2; and L=(C6H11)2P(CH22P(C6H11)2, L′= Ph2P(CH2)PPh2, Ph2P(CH2)2PPh2 cis-Ph2PCHCHPPh2, (2S,3S)-Ph2PCH- (CH3)CH(CH3)PPh2, (R)-Ph2PCH(CH3)CH2PPh2. When L=Ph2P(CH2)4PPh2 L′= Ph2P(CH23PPh2 or cis-Ph2PCHCHRPh2 the mixed ligand complexes are obtained but extensive disproportionation also occurs.

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Gordon K. Anderson

University of Missouri–St. Louis

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Vimal K. Jain

Bhabha Atomic Research Centre

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A. B. Goel

Georgia Institute of Technology

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Colin A. Fyfe

University of British Columbia

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