Alan N. Hughes

Catalytically Active Borohydride-Reduced Nickel and Cobalt Systems

Abstract Catalytic systems based upon nickel or cobalt compounds and sodium borohydride give a remarkable variety of products of wide application depending upon the reaction conditions. However, the information on these systems is widely scattered throughout the technical inorganic and organic literature. The object of this review, therefore, is to summarize and correlate what has been written about these catalytic systems and to stimulate practical industrial applications of them. Until recently, these studies were somewhat empirical in nature and we will therefore review in addition recent studies concerning the complex mechanism of Ni11 and CO11 reductions with borohydride ion. Particular attention will be given to recently published organoruckel and organocobalt complex compound structures (of as yet unexamined catalytic activity) prepared from the appropriate M11 salts and sodium borohydride in the presence of a variety of ligands.

An Efficient and Selective Monohydrido Rhodium(I) Homogeneous Hydrogenation Catalyst Containing a Cyclic Phosphine

The preparation of the complex RhH(DBP)4 (where DBP is a dibenzophosphole derivative) is described. It is a very effective and selective catalyst for the homogeneous hydrogenation of terminal olefins. Kinetic and mechanistic data for the hydrogenation of 1-hexene are presented.

Reactions of FeIII with LiAlH4 and LiBH4 in the presence of bis(diphenylphosphino)methane (dppm) and CO. The crystal and molecular structures of trans-[Fe(Cl)(CO)(η2-dppm)2] [FeCl4], trans-Fe(H)2(η2-dppm)2 and cis-[Fe(η2-S2CH(η2-dppm)2]BF4

Abstract Reactions between FeIII, dppm, CO as appropriate and LiAlH4 produce the FeII complexes trans-[Fe(Cl)(CO)(η2-dppm)2] [FeCl4]. (1a) trans-[Fe(H)2(η2-dppm)2] (2) and trans-[Fe(H)(Cl)(η2-dppm)2] (3), depending upon the reaction conditions. The trans octahedral structures, with chelating dppm ligands, of 1a and 2 have been established by X-ray crystallography. Compound 2 reacts with CO to produce the Fe0 complex Fe(CO)3(η1-dppm)2 (4), identified by NMR spectrometry, and with H2HBF4·Et2O to give the dihydrogen complex trans-[Fe(H)(η2-H2)(η2-dppm)2]BF4 (5). The dihydrogen can be replaced with, for example, CO and CH3CN to give trans-[Fe(H)(L)(η2-dppm)2]BF4 (L = CO, 6, and L = CH3CN, 7, respectively). With CS2, insertion into the Fe—bond of 5 occurs to produce the dithioformato complex cis-[Fe(η2-S2CH)(γ2-dppm)2]BF4 (8), the structure of which is also reported.

Kinetics of liquid-phase hydrogenation of 1-alkenes over a partially hydrogenated nickel boride and the effect of catalyst poisons upon these hydrogenations

Abstract The hydrogenation of several alkenes in ethanol over nickel “boride” catalysts, prepared by sodium borohydride reductions of nickel salts under various conditions, is discussed. A kinetic study has been made of the hydrogenation of 1-octene and 1-hexadecene with a partially hydrogenated catalyst designated as P-3Ni and, in the studies with 1-octene, the effects of catalyst poisons such as phosphines, n-butanethiol, and thiophene have been investigated. The results indicate that the alkene is strongly adsorbed on the catalyst surface, hydrogen is weakly adsorbed, and the rate-determining step in the hydrogenation is hydrogen transfer from solution to active sites on the catalyst. Some alkene isomerization also occurs during hydrogenation and lattice hydrogen in the catalyst appears to be involved at least in the early stages of hydrogenation. P-3Ni is relatively resistant to poisoning and probable mechanisms for catalyst poisoning by n-butanethiol and thiophene are discussed. Where possible, comparisons with the behavior of Raney nickel are made.

A convenient synthetic route to bi- and tri-nuclear palladium and platinum complexes. The crystal structures of [M3(μ3-CO)(Cl) (μ-dppm)3]Cl, MPd, Pt, dppm = bis(diphenylphosphino)methane

Abstract Simple new one-pot syntheses from metal salts, CO, dppm and NaBH 4 and the crystal structures of [M 3 ( μ 3 -CO)Cl)( μ -dppm) 3 ]Cl (M Pd, Pt) are reported. The structure of the triangulo Pd 3 -containing cation is very similar to that already reported with a CF 3 COO − anion, including the disorder at the CO and Cl ligands. There is no disorder in the Pt cation. The CO asymmetrically caps one side of the Pt 3 face and the Cl − ligand on the other side is weakly associated with only one of the Pt atoms. Convenient, high-yield syntheses of additional Pt-dppm and Pt-dppm-CO complexes are also reported.

The kinetics and mechanism of the homogeneous hydrogenation of 1-hexene catalyzed by hydridotetrahydroboratotris-(triphenylphosphine)ruthenium (II)

Abstract The first detailed kinetic study of a hydrogenation catalyzed by a metal-coordinated BH4-phosphine complex is reported. The kinetics of the hydrogenation of 1-hexene in benzene at 20 °C, at atmospheric pressure and catalyzed by RuH(BH4)(PPh3)3, has been studied, and the reaction proceeds by the unsaturate route, i.e., dissociation of the catalyst, formation of an alkyl complex, and then oxidative addition of hydrogen in a rate-determining step. The activity of this complex is compared with that of other related ruthenium catalysts.

New bis(diphenylphosphino)methane-bridged d10-d10 heterobinuclear complexes derived from Ni(Co)2(η1-Ph2PCH2 PPH2)2 and Ni2(μ-CO)(CO)2(μ-Ph2PCH2PPH2)2: The crystal structure of NiCu(CO)2(μ-Ph2PCH2PPh2) 2(BH3CN)

Abstract Syntheses of the d 10 - d 10 ionic complexes [NiCu(CO) 2 (μ-dppm) 2 (MeCN) 2 ]X (dppm = Ph 2 PCH 2 PPh 2 , X = ClO 4 , BPh 4 or PF 6 ), containing four-coordinate copper, and the related complex NiCu(CO) 2 (μ-dppm) 2 (BH 3 CN) from reactions of Ni(CO) 2 (η 1 -dppm) 2 with copper(I) species are reported as is the crystal structure of the second of these compounds. This shows a tetrahedral arrangement about nickel(O), a slightly distorted trigonal planar arrangement about copper(II), a Ni—Cu distance [3.171(4) A] which is too great for significant metal-metal interaction, and a cradle type of arrangement for the Ni—Cu-dppm framework in the solid state. Attempts to prepare related d 10 - d 10 Ni(O)—M(I or II) (M = Ag, Au, Zn or Hg) complexes by similar methods were not successful but a Ni—Au complex of limited stability can be identified in related reactions involving Ni 2 (μ-CO) (CO) 2 (μ-dppm) 2 .

Optimized Geometries and Pyramidal Inversion in s3l3-Phosphole: A Brief Theoretical Treatment

Optimized geometries and total energies for the pyramidal and planar conformations of σ 3 λ 3 -phosphole have been calculated by ab initio methods using the 6-311G * basis set and the GAUSSIAN 86 series of programs. The inversion barrier is calculated to be 24.4 kcal/mol

Rapid phosphorus–carbon bond cleavage in bis(diphenylphosphino)methane under very mild conditions: a one-step synthesis of µ-PPh2, µ-Ph2PCH2PPh2 binuclear CoI and NiI carbonyls directly from CoII and NiII salts

CoII and NiII react rapidly with NaBH4 in the presence of bis(diphenylphosphino)methane (dppm) under CO at or below (0 °C) room temperature to yield complexes of the types Co2(µ-H)(µ-PPh2)(µ-dppm)(CO)4, Co2(µ-H)(µ-PPh2)(µ-dppm)2(CO)2, and [Ni2(µ-PPh2)(µ-dppm)2(CO)2]X (X = Cl, BPh4).

Some reaction chemistry of trans-[Fe(H)(η2-H2)(η2-dppm)2] [BF4]. The crystal and molecular structure of trans-[Fe(H)(CH3CN)(η2-dppm)2] [BF4], dppm=bis(diphenylphosphino)methane

Substitution of H 2 by ligands (L) in either pure trans -[Fe(H)( η 2 -H 2 )( η 2 -dppm) 2 ] [BF 4 ], 1, or solutions of [Fe(H) 2 (dppm) 2 ] 2, L and HBF 4 .Et 2 O in which 1 is made in situ , produce the compounds trans -[Fe(H)(L)( η 2 -dppm) 2 ] [BF 4 ] (LCH 3 CN, 3; succinonitrile, 4; pyridine, 5; C 2 H 4 , 6; and N 2 , 7). The order of H 2 replacement from 1 appears to be CH 3 CN>N 2 >C 2 H 4 ∼pyridine. Evidence is presented for the protonation of the hydride ligands of 1 or 2 to produce [Fe(H 2 ) 2 ( η 2 -dppm) 2 ] [BF 4 ] 2 , 8, although 8 could not be fully characterized nor could it be obtained in the solid state. Trans -[Fe(CH 3 CN) 2 ( η 2 -dppm) 2 ] [BF 4 ] 2 , 9, was obtained from solutions of 8 treated with acetonitrile. The coordination geometries of 3, 9 and 4 (monodentate succinonitrile) have been confirmed by X-ray crystallography (only the gross structural features of 4 were obtained due to a poor data set from a very small crystal).