Andreas Roodt

Structure and solution behaviour of rhodium(I) Vaska-type complexes for correlation of steric and electronic properties of tertiary phosphine ligands

Abstract This paper deals with the synthesis of rhodium(I) Vaska-type complexes of the general form trans-[Rh(CO)X(PX3)] (X=halide, X aryl or alkyl substituent) when incorporating tertiary phosphine ligands and illustrates their simple application as probes to evaluate steric and electronic effects, specifically in tertiary phosphine ligands, analogous to the Tolman model. They are easy to prepare and do not exhibit the toxicity as the corresponding nickel complexes, while structural and infrared data can be conveniently utilised to estimate ligand properties with relative ease. These Vaska-type complexes are often obtained as by-products when reacting [Rh(μ-Cl)(CO)2]2 with bidentate ligands in non-stoichiometric amounts, thus yielding unreacted dimer, which, upon addition of the tertiary phosphine, quantitatively converts to the Vaska-type complex. A representative summary of rhodium(I) Vaska-type systems is reported and structures correlated with steric and electronic properties of related literature complexes. Selected aspects of reactions of the corresponding arsine and stibine analogues are illustrated and solvent effects on equilibrium behaviour as well as the iodomethane oxidative addition described.

Steric effects induced by ferrocenyl in tertiary organophosphines: crystal structure of trans-chloromethylbis(ferrocenyldiphenylphosphine)palladium(II) benzene disolvate

Abstract The structure determination of the title compound, trans -[PdMeCl(PPh 2 Fc) 2 ]·2C 6 H 6 , (PPh 2 Fc=C 22 H 19 FeP) shows the Pd(II) moiety to have a square planar geometry with the bulky phosphine ligands in a trans orientation. The compound crystallises in the triclinic space group P 1 with 1 mole per unit cell accompanied by two benzene solvent molecules. A 50% statistical disorder was observed in the methyl and chloride positions. Bond distances and angles of the coordination polyhedron are PdP=2.3328(10) A, PdCl=2.378(3) A, PdC(10)=2.108(10) A, PPdCl=92.70(9)° and PPdC(10)=86.8(4)°. The structure is compared with the isomorphous trans -[Pt(Cl) 2 (PPh 2 Fc) 2 ]·2C 6 H 6 and other relevant structures of Pt(II) and Pd(II) described in the literature. The steric demand of the PPh 2 Fc ligand was estimated from all known structures to be approximately 155° using the Tolman model.

Octacyano and Oxo- and Nitridotetracyano Complexes of Second and Third Series Early Transition Metals

Publisher Summary This chapter presents a summary on the chemistry of octacyano complexes and oxo- and nitridocyano complexes of molybdenum, tungsten, niobium, tantalum, technetium, and rhenium, with emphasis on the structural and kinetic properties. The octacyano complexes of molybdenum and tungsten are stable and inert toward substitution reactions and are suitable for theoretical studies of redox reactions and application of the Marcus theory. The oxo- and nitridocyano complexes of MO(IV), W(IV), Tc(V) , Re(V), and Os(VI) are good candidates for kinetic studies of substitution reactions with both mono- and bidentate ligands and are of interest in view of the large variations in the observed reactivity. The octacyano complexes of MO(V) and W(V) find excellent use in the oxidation of organic substances that require a mild oxidizing agent. Derivatives of the dioxotetracyano complexes of Mo(IV) and W(IV) can take up dioxygen that leads to the activation of the O2 molecule. Thus, the complexes are candidates as catalysts in oxidation reactions with dioxygen as well as oxygen-transfer reactions. The stereochemistry of octacyano complexes is concerned with the d1 and d2 ions of niobium, molybdenum, and tungsten.

Electron density manipulation in rhodium(I) phosphine complexes: structure of acetylacetonatocarbonylferrocenyl- diphenylphosphinerhodium(I)

Abstract The title complex [Rh(acac)(CO)(PPh2Fc)] (acac = acetylacetonato, PPh2Fc = ferrocenyldiphenylphosphine), was obtained in acetone by reaction of the tertiary phosphine with [Rh(acac)(CO)2] and was characterised by IR spectroscopy, 1H and 31P NMR and single crystal X-ray crystallography. This is a rare example illustrating the incorporation of the ferrocenyl moiety in a monodentate tertiary phosphine complex of rhodium(I). It crystallises in the triclinic space group P 1 with two independent molecules in the asymmetric unit and refined to R=2.40% from 5215 reflections. The independent molecules, showing the usual square planar geometry, differ mainly in the rotation mode of the asymmetric phosphine around the Rh-P bond and a slight deviation in the Rh-CO bond from linearity, which was correlated with IR data.

Structural correlation between Rh-P and Rh-C bond distances vs. 31P and 13C NMR parameters in monocarbonylphosphinerhodium(I) complexes: Crystal structure of (methyl 2-(amino)-1-cyclopentene-1-dithio arboxylato-κN, κS)-carbonyl(triphenylphosphine) rhodium(I)

Abstract The crystal structure of (methyl 2-(amino)-1-cyclopentene-1-dithiocarboxylato- κN , κS )-carbonyl(triphenylphosphine)rhodium(I), [Rh(hacsm)(CO)(PPh 3 )], was determined. The complex crystallizes in the monoclinic space group P 2 1 / c with a = 16.430(1), b = 9.930(1), c = 17.194(1) A, β = 90.72(1)°, Z = 4, R = 2.89% from refinement of 3143 reflections. The structural data obtained by this study were correlated with 31 P and 13 C NMR data measured for different [Rh(L,L′-BID)(CO)(PPh 3 )] complexes (L,L′-BID = monocharged bidentate ligand with donor atoms L, L′: variations of oxygen, nitrogen and sulphur). A good correlation between 1 J ( 31 P- 103 Rh) and the Rh-P bond distance was obtained.

Mechanism for the oxidative addition of lodomethane to carbonyl(N-hydroxy-N-nitrosobenzenaminato-O,O′)triarylphosphinerhodium(I) complexes and crystal structure of [Rh(cupf)(CO)(CH3)(1)(PPh3)]

Abstract Rh(I) complexes, [Rh(cupf)(CO)(PX 3 )] (cupf= cupferrate; PX 3 = PCy 3 , P( o -Tol) 3 , PPh 3 , PPh 2 C 6 F 5 , P( p -ClC 6 H 4 ) 3 and P( p -MeOC 6 H 4 ) 3 ), react with iodomethane to form Rh(III) alkyl compounds. The reaction was studied in the solvents Bz, EtOAc, Me 2 CO, MeOH, CH 3 CN and DMSO having different polarities and donocities. The reaction proceeds through two competing rate determining steps, one of which is first-order in [CH 3 I]. A reaction mechanism, which includes specific solvent effects, is given. The structure determination of [Rh(cupf)(CO)(CH 3 )(I)(PPh 3 )] shows the complex to crystallize in space group P 1 with a =9.912(2), b = 11.534(1), c = 12.514(2) A, α = 67.84(2), β = 84.41(2), γ = 73.15(1)°, Z = 2 and D m = 1.73 g cm −3 . The molecule has distorted octahedral geometry with CH3 and I cis -bonded. Bond distances: RhPI = 2.708(2), RhP = 2.327(4), RhO(hydroxy) = 2.04(1), RhO(nitroso) = 2.175- (9), RhC(carbonyl) = 1.81(2) and RhC(methyl) = 2.08(1) A. Rates for the slow alkyl → acyl conversion in Me 2 CO and CH 3 CN are also given for this complex.

Structure/reactivity relationships and mechanism from X-ray data and spectroscopic kinetic analysis

The development in crystallography is nothing short of phenomenal, showing an ever increasing trend towards applications, such as in molecular biology. ‘Traditional’ small molecule chemical crystallography tends to, in many aspects, be considered as trivial due to the exponential growth in computing power and the parallel expansion in software. However, many dynamic processes (still) occur at the molecular level. Thus, the fundamental understanding of subtle nuances in structural behaviour, and the associated influence on other (kinetic) properties, is often trivialized when conclusions are simply made based on thermodynamic observations alone. This review aims to emphasize the importance of crystallography in small molecule chemistry by presenting detailed evaluations of two extended ‘case studies’, i.e. the first on structure and dynamics of the middle transition metal cyanide-oxido complexes, and the second on rhodium model homogeneous catalyst precursors. Both underline the fact of understanding the overarching principles of dynamics, i.e. time-resolved behaviour of processes, but considered from a structural perspective. The reference point is to focus on an integrated and overarching mechanistic approach, utilizing structural data, but in particular reaction kinetics, to obtain a more complete picture of processes or systems being evaluated.

Chemical structure of dicaesium sodium azidooxotetracyanomolybdate(IV)

Abstract The structure of Cs2Na[MoO(CN)4(N3)] was determined by single-crystal X-ray diffraction methods from diffractometer data and refined to R = 0.051. The royal-blue crystals are orthorhombic, space group Pnma, with cell dimensions a = 15.874, b = 7.875, c = 10.371 A, Z = 4. The [MoO(CN)4(N3)]3− ion is a distorted octahedron with the Mo atom displaced 0.28 A towards oxygen from the plane containing four cyano groups. Bond distances found: MoCav = 2.17(1); MoO = 1.70(1); MoN (azido) = 2.29(2) A. The azido chain is linear and bond at an angle of 121(1) ° with Mo. The sodium ion has an octahedral environment, whilst caesium ions display distorted six- and nine-atom environments respectively.

First structural confirmation of different geometrical isomers in the same crystal lattice: the crystal structure of benzoylacetonatocarbonyltriphenylphosphinerhodium(I)

Abstract The first structural confirmation of two different [Rh(BA)(CO)(PPh3)] isomers (BA = benzoylacetonate, CH3(CO)CH(CO)C6H5), namely one with PPh3 cis to the oxygen atom nearest to the phenyl group and the second isomer with PPh3 trans to the oxygen nearest to the phenyl group, in the same crystal lattice is reported. The small influence of the different substituents is illustrated by the near equal RhO, RhP and RhC bond distances in the two different isomers. The structure crystallizes in the triclinic system, space group P 1 with a = 15.625(2), b = 19.138(2), c = 8.891(2) A , α = 95.66(1), β = 74.43(1), γ = 90.52(1)° and Z = 4 . The RhP, RhCO and RhO bond distances for isomer I are 2.249(3), 1.739(14), 2.032(8) and 2.079(8) A. respectively, while the corresponding bond distances for isomer II are 2.248(3), 1.768(14), 2.018(8) and 2.057(7) A, respectively.

The crystal structure of tetraethylammonium aquatetracyanooxorhenate(V)

SummaryThe crystal structure of the tetraethylammonium salt of [ReO(H2O)(CN)4]− has been determined from threedimensional x-ray diffraction data. The light blue crystals are monoclinic, space group P21/m witha=8.760(1),b=9.518(5),c=11.718(1) Å, β=102.63(1)o with two molecules per unit cell. The final R value using 2009 observed reflections and anisotropic thermal parameters for all the non-hydrogen atoms was 0.038. The [ReO(H2O)(CN)4]− ion has a distorted octahedral geometry with the rhenium atom displaced by 0.30 Å out of the plane formed by the four carbon atoms of the cyano ligands towards the oxo ligand. Bond distances: Re=O=1.667(8), Re−OH2=2.142(7) and Re−C (average)=2.11(1) Å.