Brian R. James

The reactivity of five-coordinate Ru(II) (1,4-bis(diphenylphosphino)butane) complexes with the N-donor ligands: ammonia, pyridine, 4-substituted pyridines, 2,2′-bipyridine, bis(o-pyridyl)amine, 1,10-phenanthroline, 4,7-diphenylphenanthroline and ethylenediamine

Abstract A series of Ru(II)(1,4-bis(diphenylphosphino)butane)(L)2 complexes was synthesized from [RuCl2(dppb) l2 (μ-dppb) or RuCl2 (dppb)- (PPh3); dppb = Ph2P(CH2)4PPH2, L = NH3, pyridine (py), 4-aminopyridine (4-NH2py), 4-cyanopyridine (4-CNpy), 4-dimethylaminopyridine (4-Me2Npy), 4-methylpyridine (4-Mepy), 4-phenylpyridine (4-Phpy), 4-vinylpyridine (4-Phy) and N-methylimidazole (Melm) and L2 = 2,2′-bipyridine (bipy), bis(o-pyridyl)amine (bpa), 1,10-phenanthroline (phen), 4,7-diphenylphenanthroline (or bathophenanthroline, batho) and ethylenediamine (en). The complexes were characterized by elemental analysis, cyclic voltametry, UV-Vis, NMR and IR spectroscopies. The structures of trans-RuCl2(dppb) (py)2 (3), cis-RuCl2(dppb)(bipy) (4) and cis-RuCl2(dppb) (phen) (5) were established by X-ray crystallographic analyses. Crystals of trans-3, cis-4-CH2Cl2 and cis-5-solvate are all monoclinic, space group P21/c, with Z=4; a = 12.946 (2), b = 14.204(3), c = 18.439(4) A , β = 90.08(2)° for trans-3; a=10.694(6), b=18.485(6), c=18.632(7) A , β = 90.26(3)° for cis-4·CH2Cl2; a = 17.094 (1), b = 9.923(2), c = 21.905(2) A , β = 98.883 (6)° for cis-5 solvate. The structures were solved by the heavy atom Patterson method and were refined by full-matrix least-squares procedures to R=0.069, 0.071 and 0.036 (Rw = 0.069, 0.076 and 0.039) for 1957, 4165 and 4824 reflections with l ≥ 3σ (l), respectively.

Synthesis of chiral amines catalyzed homogeneously by metal complexes

Abstract This review describes developments in catalytic asymmetric hydrogenation of prochiral imines. The homogeneous systems were initially dominated by ones based on Rh complexes containing chiral, chelating diphosphine ligands, although related Ru- and Ir-based systems are becoming more prominent; a very recent, extremely effective hydrogen transfer system (from formic acid), based on Ru catalysts containing chiral 1,2-diamine ligands, is especially significant. A fundamentally different type involving an early transition-metal catalyst (a chiral titanocene) has been reported. Enantiomeric excess (e.e.) values in the range of 90–100% have now been achieved with certain substrates. Emphasis is given to some Rh and Ru catalysts developed in the Department of Chemistry, The University of British Columbia (UBC). Factors discussed include: dependence of conversions, rates and e.e. values on substrate and catalyst type; kinetic dependences; and mechanistic insights, especially possible roles of intermediate metal-hydride and -imine species.

Novel and Improved Syntheses of 5,15-Diphenylporphyrin and its Dipyrrolic Precursors

Optimized syntheses of 5,15-diphenylporphyrin (DPP, 1) and its dipyrrolic precursors are described. A novel procedure for the synthesis of dipyrromethane (2), prepared by hydrodesulfurization of the corresponding di-2-pyrrolylthione (8), is presented, as well as an improved method to isolate large quantities of 5-phenyldipyrromethane (4), prepared by the acid-catalysed condensation of pyrrole with benzaldehyde. These dipyrromethanes are key reagents in two high-yield (2a2)-type syntheses of DPP. 5-Phenyldipyrromethane was formylated to provide 1-formyl- (11) and 1,9-diformyl-5-phenyldipyrromethane (12), and reduction of 11 provided the corresponding hydroxymethyl compound 13. These compounds (11-13), however, were much less efficient precursors to DPP. Two polypyrrolic compounds, 1,1,2,2-dipyrrolylethane (9) and 5,10- diphenyltripyrrane (10), potentially useful for the synthesis of porphyrinic macrocycles, were isolated as side- products during the dipyrromethane and 5-phenyldipyrromethane syntheses. # 1998 John Wiley & Sons, Ltd.

Hydrogenation Reactions Catalyzed by Transition Metal Complexes

Publisher Summary This chapter focuses on the hydrogenation reactions catalyzed by transition metal complexes, with the aim of developing catalysts for selective hydrogenation under mild conditions. Olefin hydrogenations—for example—are important industrial processes, and selectivity is critical to the success of such processes. Greater product selectivity has an important impact on energy and resource utilization in terms of reduced process energy requirements for product separation and purification, and in terms of low-value byproducts. The advances in asymmetric hydrogenation—a stereospecific selectivity—have been notable, and an understanding of the detailed pathways is just beginning to emerge, although much remains to be done, and matching of substrates with the most suitable chiral catalyst still remains an empirical art. The chapter demonstrates the degree of understanding that can be attained for a homogeneous hydrogenation catalyst at the molecular level. Enantiomeric products are used widely in the pharmaceutical industry and as food additives, and the production of either the natural or nonnatural amino acids is at least one advantage shown by the organometallic catalysts compared to enzyme systems. The incorporation of an effective rhodium catalyst into a protein begins to bring closer together analogies between the two areas. Interest is growing in chiral catalysts based on less expensive metals, such as cobalt, and a wider range of chiral ligands–including naturally occurring ones, is being exploited.

Activation of dihydrogen by ruthenium(II)-chelating phosphine complexes, and activation of dioxygen by ruthenium(II) porphyrin complexes: an update

Abstract This presentation reviews some recent studies from these laboratories that concern activation of dihydrogen and of dioxygen by various ruthenium complexes in solution. Part 1 describes developments in the catalytic chemistry of Ru(II)/chelating ditertiary phosphine complexes, in particular their applications in asymmetric hydrogenation, while Part 2 outlines work on O 2 -oxidation of thioethers catalyzed by Ru(II) porphyrin complexes. An experimental section, giving full details on the syntheses and characterization of the complexes, including X-ray crystallographic analyses, and on the catalysis experiments, is not given in this paper; such details will appear in future publications, but are meanwhile available on request.

The synthesis, structural characterization, and in vitro anti-cancer activity of chloro(p-cymene) complexes of ruthenium(II) containing a disulfoxide ligand

Abstract Two diruthenium(II) complexes [RuCl2(p-cymene)]2(μ-BESE) (1), [RuCl2(p-cymene)]2(μ-BESP) (2), and the mononuclear salt [RuCl(p-cymene)(BESE)]PF6 (3), containing the disulfoxides BESE and BESP, were synthesized and characterized by elemental analysis, and NMR and IR spectroscopies, and were shown to contain S-bound sulfoxide groups; the disulfoxides are EtS(O)(CH2)nS(O)Et, where n=2 (BESE) or 3 (BESP). Complexes 1 and 3 were also characterized by X-ray crystallography. Preliminary in vitro tests of 1 and 3 were conducted using the MTT assay, which measures mitochondrial dehydrogenase activity as an indication of cell viability; these complexes showed in vitro anti-cancer activity against a human mammary cancer cell line (MDA-MB-435s) with IC50 values of 360 and 55 μM, respectively.

Synthesis, characterization and reactivity of some mono- and dinuclear chlororuthenium complexes containing chelating ditertiary phosphines (PP) with PP:Ru=1

Mixed-valence complexes of the type (PP)ClRu(μ-Cl) 3 RuCl(PP), and the [RuCl(PP)] 2 (μ-Cl) 2 products formed by their reduction with H 2 , are synthesized, where PP is a chelating ditertiary phosphine Ph 2 P(CH 2 ) n PPh 2 (n=3–6) or some related chiral analogues such as diop, chiraphos, dppcp, dpcycp, bdpp, binap, phenop or norphos (diop=Ph 2 PCH 2 HCH 2 PPh 2 ; chiraphos=Ph 2 PCH(Me)CH(Me)PPh 2 ; dppcp=Ph 2 P HPPh 2 ; dpcycp=(C 6 H 11 ) 2 P HP(C 6 H 11 ) 2 ; bdpp(skewphos)=Ph 2 PCH(Me)CH 2 CH(Me)PPh 2 ; binap=2,2′-bis(diphenylphosphine)-1,1′-binaphthyl; phenop=Ph 2 PN(Et)CH(CH 2 Ph)CH 2 OPPh 2 ; norphos=Ph 2 P HPPh 2 ). The [RuCl(binap)] 2 (μ-Cl) 2 species is also formed in solution by dissociation of PPh 3 from RuCl 2 (binap)(PPh 3 ) which is synthesized by phosphine exchange with RuCl 2 (PPh 3 ) 3 . From the [RuCl(PP)] 2 (μ-Cl) 2 complex (PPPh 2 (CH 2 ) 4 PPh 2 ), a range of L(P-P)Ru(μ-Cl) 3 RuCl(PP) species is readily formed, where L includes an amine, acetone, N,N-dimethylacetamide, MeI, PhCN, CO, N 2 or H 2 ; the LNEt 3 adduct is made also from RuCl 2 (dppb)(PPh 3 ), while the corresponding dimethyl sulfoxide adduct (LDMSO), 17e , is synthesized directly from cis - RuCl 2 (DMSO) 4 and the phosphine. 31 P{ 1 H} NMR data are presented for the Ru(II) species, while characterization of 17e includes an X-ray crystallographic analysis that confirms the trichloro-bridged formulation. Crystal data are as follows: triclinic, P , a =12.796(1), b =14.559(1), c =18.429(1) A, a =103.983(5), β=99.634(6), γ=99.634(6)°, Z =2, R =0.037 and R w =0.046 for 9088 reflections with I ≥ 3σ( I )

Homo- and Heterobimetallic Precursor Catalysts for the Heck Reaction, and a Proposal for a General Catalytic Cooperativity Index

Homo- (Pd2) and heterobimetallic (PtPd) complexes supported by a P,P-bridging, bis(P,N-chelating) coordination mode of the potentially hexadentate ligand 1,1-bis[di(o-N,N-dimethylanilinyl)phosphino]methane (dmapm) are effective catalyst precursors for the aerobic Heck coupling of iodobenzene and styrene at 100 °C in DMF/H2O solution containing K2CO3. This medium allows for trivial separation of the trans-stilbene product which precipitates after the reaction mixture is cooled. The bimetallic precursors are more active than predicted from the sum of the activities of complexes chosen to mimic their mono-metallic “half units,” suggesting some degree of intermetallic cooperativity during the reaction. A non-linear dependence of initial rate on catalyst concentration implies, however, that the complexes do not remain intact, and may be involved in dissociative equilibria with non-dmapm containing monometallic components that are more active species for the Heck coupling. The complexes are slowly degraded by oxidation at a phosphorus centre. A general index for quantifying the degree of intermetallic cooperativity during a catalytic cycle is proposed and its utility and limitations are discussed.

A comparison of catalytic activity for imine hydrogenation using Ru ditertiary phosphine complexes, including chiral systems

Abstract A family of ruthenium ditertiary phosphine complexes was investigated for catalytic activity toward imine hydrogenation. The diphosphines (PP) used include chiral (chiraphos, diop, binap) and achiral (dppe, dppb) systems (chiraphos=Ph2PCH(Me)CH(Me)PPh2; diop=Ph2PCH2{ CHOCMe 2 O C}HCH2PPh2; binap=2,2′- bis(diphenylphosphino)-1,1′-binaphthyl; Ph2P(CH2),:PPh2 (n=2, dppe; n=4, dppb)). Activity was observed in MeOH at low catalyst concentrations (0.77 mM Ru), under moderate conditions (room temperature (r.t.), 1000 psi H2). The air-stable Ru2Cl5(PP)2 complexes were more active than the commonly used dimeric Ru2(II,II) systems to which they give rise in situ. Asymmetric induction in the prochiral ketimine PhCH2NC(Me)Ph was consistent, though modest, within the diop and binap series of neutral complexes, implying a common catalytic intermediate within each series. A maximum e.e. of 27% was found using Ru2Cl5(chiraphos)2 as catalyst; this represents a non-optimized figure for asymmetric induction, as no other prochiral ketimines were screened.

Catalytic decarbonylation, hydroacylation, and resolution of racemic pent-4-enals using chiral bis(di-tertiary-phosphine) complexes of rhodium(I)

Abstract Attempts to decarbonylate racemic aldehydes catalytically using rhodium(I) complexes containing chiral di-tertiary-phosphine ligands are described. Incorporation of an alkenic moiety into the aldehyde, for subsequent probing of induced asymmetry by chiral shift reagents, leads instead to formation of optically active hydroacylated products via kinetic resolution of the precursor racemic aldehyde. For example, ( RS )-2-methyl-2-phenylpent-4-enal ( 1a ) yields, on treatment with [Rh( S,S -chiraphos) 2 ]Cl, 2-methyl-2-phenylcyclopentanone with up to 69% e.e. of the (−)-(S) optical isomer and remaining unreacted aldehyde which is possibly the enantiomerically pure (−)-(R) form. Extension of this cyclization reaction to a 3,3-disubstituted pent-4-enal similarly provides a synthesis for an optically active 3,3-disubstituted cyclopentanone. Decarbonylation by-products are also observed; those from 1a appear as E - and Z -2-phenylpent-2-ene. The cyclization of 1a is catalyzed also by Rh(chiraphos)(solvent) 2 + but with lower e.e.