Laurence Carlton

Reactions of [Rh(Tp*)(PPh3)2] (Tp* = hydrotris(3,5-dimethylpyrazolyl)-borate) involving fragmentation or loss of Tp*. Structures of [Rh(Cl)2(H)(PPh3)2(pz*)], [(PPh3)2Rh(μ-SC6F5)2Rh (SC6F5)(H)(PPh3)(pz*)] (pz* = 3,5-dimethylpyrazole) and [{Rh(Cl)2(PPh3)2}2Hg]

Abstract The complex [Rh(Tp*)(PPh3)2] reacts with dichloromethane to give [Rh(Cl)(H)2(PPh3)2(pz*)] (1) and [Rh(Cl)2(H)(PPh3)2(pz*)] (2), with C6F5SH to give [(PPh3)2Rh(μ-SC6F5)2Rh(SC6F5)(H)(PPh3)(pz*)] (3) and with HgCl2 to give [{Rh(Cl)2(PPh3)2}2Hg] (4), all under mild conditions. The crystal structures show that 2 has a slightly distorted octahedral geometry, 3 has approximately square planar Rh(I) and octahedral Rh(III) geometries, with an angle of 160.7° between the two RhS2 planes and 4 has rhodium with a square pyramidal geometry where mercury occupies a position at the apex of the pyramid; the Rh–Hg–Rh geometry is linear and, with respect to the Rh–Hg–Rh axis, the ligands (Cl, PPh3) on one rhodium are offset by approximately 42° relative to their counterparts on the second rhodium. In 2 an intramolecular hydrogen bond exists between the pyrazole NH and one of the chloride ligands. Structure 4 is unusual in that it contains an unsupported mercury bridge.

Influence of ligand polarizability on the reversible binding of O2 by trans-[Rh(X)(XNC)(PPh3)2] (X = Cl, Br, SC6F5, C2Ph; XNC = xylyl isocyanide). Structures and a kinetic study.

The complexes trans-[Rh(X)(XNC)(PPh 3) 2] (X = Cl, 1; Br, 2; SC 6F 5, 3; C 2Ph, 4; XNC = xylyl isocyanide) combine reversibly with molecular oxygen to give [Rh(X)(O 2)(XNC)(PPh 3) 2] of which [Rh(SC 6F 5)(O 2)(XNC)(PPh 3) 2] ( 7) and [Rh(C 2Ph)(O 2)(XNC)(PPh 3) 2] ( 8) are sufficiently stable to be isolated in crystalline form. Complexes 2, 3, 4, and 7 have been structurally characterized. Kinetic data for the dissociation of O 2 from the dioxygen adducts of 1- 4 were obtained using (31)P NMR to monitor changes in the concentration of [Rh(X)(O 2)(XNC)(PPh 3) 2] (X = Cl, Br, SC 6F 5, C 2Ph) resulting from the bubbling of argon through the respective warmed solutions (solvent chlorobenzene). From data recorded at temperatures in the range 30-70 degrees C, activation parameters were obtained as follows: Delta H (++) (kJ mol (-1)): 31.7 +/- 1.6 (X = Cl), 52.1 +/- 4.3 (X = Br), 66.0 +/- 5.8 (X = SC 6F 5), 101.3 +/- 1.8 (X = C 2Ph); Delta S (++) (J K (-1) mol (-1)): -170.3 +/- 5.0 (X = Cl), -120 +/- 13.6 (X = Br), -89 +/- 18.2 (X = SC 6F 5), -6.4 +/- 5.4 (X = C 2Ph). The values of Delta H (++) and Delta S (++) are closely correlated (R (2) = 0.9997), consistent with a common dissociation pathway along which the rate-determining step occurs at a different position for each X. Relative magnitudes of Delta H (++) are interpreted in terms of differing polarizabilities of ligands X.

An NMR study of trans ligand influence in rhodium η2 triphenyltin hydride complexes

The complex [Rh(O2Cisoq)(H)(SnPh3)(PPh3)2] (O2Cisoq = isoquinoline-1-carboxylate), characterized by x-ray crystallography, was used as a precursor to three-center bonded complexes [Rh(O2Cisoq)(η2-HSnPh3)(PPh3)(4-Rpy)] (R = carbomethoxy, acyl, bromo, aldehyde, hydrogen, methoxy, dimethylamino), which were prepared in situ from the bis(phosphine) complex in dichloromethane by addition of the pyridine. Of two isomeric forms of [Rh(O2Cisoq)(η2-HSnPh3)(PPh3)(4-Rpy)], one, with 4-Rpy positioned trans to tin, is formed at 0°C; the other, with isoquinoline positioned trans to tin, is formed by partial (25–50%) conversion of the first isomer (in solution) upon warming to 30–35°C for a few minutes. The relative coordination geometries of the two isomers were established by using a 15N-enriched pyridine. NMR parameters (1H, 31P, 103Rh, and 119Sn) for the pyridine-containing complexes show trends consistent with a significantly greater SnH interaction in complexes having isoquinoline lying trans to tin and a threshold of σ donor strength for the pyridine below which the influence on Rh(SnH) bonding is minimal and above which the influence is to enhance the SnH interaction. Possible reasons for these effects are discussed.

Substituted cyclopentadienyl complexes. Part 4. The catalysed synthesis and proton nuclear magnetic resonance spectra of [Ru(η5-C5H4Me)(CO)(L)I] and [Ru(η5-C9H7)(CO)(L)I](L = phosphine or isocyanide) and the crystal structure determination of [Ru(η5-C9H7)(CO){P(CH2Ph)3}I]

The reaction between [Ru(η5-C5H4Me)(CO)2I] and L [L = P(OMe)3, P(OEt)3, P(OPri)3, PPh3, PMe2Ph, ButNC, or 2,6-Me2C6H3NC] or [Ru(η5-C9H7)(CO)2I] and L [L = P(OMe)3, P(OEt)3, P(OPri)3, P(OC6H4Me-o)3, PPh3, or P(CH2Ph)3] in the presence of [{Fe(η5-C5H5)(CO)2}2] as catalyst yields the new substituted products [Ru(η5C5H4Me)(CO)(L)I], (1) and [Ru(η5-C9H7)(CO)(L)I], (2). The new products have been characterized by a combination of i.r. and n.m.r. spectroscopy and mass spectrometry. Ring proton resonances of complexes (1) have been assigned by nuclear Overhauser enhancement (n.O.e.) spectra [L = P(OMe)3, PMe2Ph, PMePh2, or 2,6-Me2C6H3NC]. The n.O.e. spectra also reveal preferential conformations of the cyclopentadienyl ring when L is large. Such spectra were also recorded for complexes (2)[L = P(OC6H4Me-o)3 or P(CH2Ph)3] and together with coupling constant data are consistent with a ligand orientation in which L = P(CH2Ph)3 is found preferentially under the central carbon atom of the cyclopentadienyl indenyl ring. This was further confirmed by a crystal structure determination of [Ru(η5-C9H7)(CO){P(CH2Ph)3}I]·0.5C6H6: space group P, Z= 2, a= 9.923(2), b= 11.055(4), c= 14.543(3)A, α= 84,52(2), β= 77.72(2), γ= 82.74(2)°, and R= 0.0560.

The 15N NMR spectra of some dihydrobis(triphenylphosphine)rhodium(III) complexes of aromatic N-donor carboxylates

Abstract 15 N (natural abundance) NMR spectral data are reported for a series of complexes [RhH 2 (PPh 3 ) 2 (NArCO 2 )] (NArCO 2 = pyridine-2-carboxylate, 6-methyl- pyridine-2-carboxylate, pyrazine-2-carboxylate, quinoline-2-carboxylate, isoquinoline- 1-carboxylate, and quinoxaline-2-carboxylate), and were obtained by the INEPT method with polarisation transfer from the hydride lying trans to nitrogen. The 15 N signal moves upfield by 35–50 ppm up on coordination of nitrogen to the metal, 2 J ( 15 N- 1 H trans ) has a value of ca. 25 Hz, and 1 J ( 103 Rh- 15 N) lies in the range 9.1–10.1 Hz.

Rhodium-103 NMR of Carboxylate and Thiolate Complexes by Indirect Detection using Phosphorus

Fifty four carboxylate and thiolate complexes of rhodium including [Rh(O2CR)(PPh3)3] (R=CH3, CF3), [Rh2(SC6F5)2(PPh3)4] and derivatives obtained by reaction with hydrogen, pyridine and methyldiphenylphosphine, [Rh(O2CArN)(H)2(PPh3)2] (O2CArN=pyridine‐2‐carboxylate and related chelating ligands) and complexes prepared in situ (many as mixtures) by the reaction of [Rh(H)(PPh3)4] with various thiols were studied by two‐dimensional inverse 103Rh–31P correlated NMR (HMQC). Rhodium chemical shifts were found to fall within the range 840 to ‐422 ppm. Trends in δ103Rh for thiolate and carboxylate complexes are similar but not identical, with somewhat lower δ for most of the thiolates, increasing in the approximate order [Rh(SR)(H)2(PPh3)3]<[Rh(SR)(PPh3)3], cis‐[Rh(SR)(PPh3)2(py)]<[Rh2(SR)2(PPh3)4]<[Rh(SR)(H)2(PPh3)2(py)]<[Rh(SR)2(H)(PPh3)2(py)].

Substituted cyclopentadienyl complexes: II. 13C NMR spectra of some [(η5-C5H4Me)Fe(CO)(L)I] complexes

Abstract The 13 C { 1 H} NMR spectra of a series of complexes [(η 5 -C 5 H 4 Me)Fe(CO)(L)I] (L  t-BuNC, P(OMe) 3 , PMe 3 , PMe 2 Ph, PMePh 3 , PPh 3 and P(C 6 H 11 ) 3 ) have been recorded and the five cyclopentadienyl resonances assigned to ring carbon atoms by means of CH correlated spectra. It has been observed that the C atoms ortho to the ring methyl group (C(2) and C(5)) as well as the quaternary C atom are always coupled to the ligand P atom. A correlation between the chemical shift difference Δ(C(2) – C(5)) and the Tolman cone angle, θ, has also been established.

Rhodium-103 NMR

Abstract Developments in 103Rh NMR from the first directly observed high-resolution spectrum to the use of indirect detection methods, parahydrogen-induced polarisation (PHIP)-enhanced measurements and the first solid-state CP-MAS 103Rh spectrum are described together with influences on the chemical shift arising from ligand properties, temperature, solvent, intramolecular rearrangements, diastereomerism and secondary isotope effects. Correlations between δ(103Rh) and stability and rate constants, structural and steric parameters, Hammett σ and infrared data are discussed as is the use of 103Rh NMR in other aspects of rhodium chemistry relevant to catalysis, namely high-pressure studies and metal clusters. Methods of calculating chemical shifts and of determining the signs of coupling constants are noted. Rhodium-103 chemical shifts are given for more than a thousand complexes and clusters together with coupling constants for complexes showing spin coupling of 103Rh to 1H, 13C, 15N, 19F, 29Si, 31P, 77Se, 119Sn, 125Te and to 103Rh and other metals.

An investigation of steric effects along a cyclopentadienyl substituent: a study by 1H, 13C and 29Si NMR spectroscopy of bis(trimethylsilyl)cyclopentadienyl iron complexes

Abstract The syntheses of a range of complexes, [(η 5 -C 5 H 3 (SiMe 3 ) 2 )Fe(CO)(L)I], (L  t BuNC, 2,6-Me 2 C 6 H 3 NC (xylNC), P(OMe) 3 , PMe 2 Ph, P(O- o -tol) 3 PPh 3 , P( m -tol) 3 , P( p -tol) 3 , and P(CH 2 Ph) 3 ) are reported. Three separate cyclopentadienyl ring proton resonances were observed in the NMR spectra of the iron complexes, and their assignments determined from NOE experiments (L  P(OMe) 3 , P(O- o -tol) 3 ). The 13 C NMR spectra were recorded and assignments made from a knowledge of the 1 H spectra by use of CH correlated spectroscopy. 29 Si and 31 P NMR data were also obtained. Three-dimensional correlations were observed between separations of pairs of NMR resonances ( 29 Si, 13 C and 1 H) and (i) steric effects as measured by the Tolman cone angle, θ, and (ii) electronic effects as measured by ν CO , the stretching frequency of the carbonyl group. The degree of correlation varied with the distance of the NMR-active nuclei from the iron atom (ring C and Si(CH 3 ) 3 Si, C and H atoms), and the result is taken as an indication of the best region, in space, in which the Tolman cone angle concept is most appropriate. The best correlation occurred between the chemical shift difference of the two 29 Si resonances and θ and ν(CO) ( R 2 = 0.96, mse = 0.00640). Conformational data obtained from the NOE spectra suggest that the Group 15 donor ligand resides close to a SiMe 3 group and near the two adjacent ring protons. The steric demand of the two bulky SiMe 3 groups hinders rotation of the P(OMe) 3 and P(O- o -tol) 3 ligands around the ring, resulting in a windscreen wiper motion of the ligand between the two SiMe 3 groups.

Activation of EH (E=Sn, Si, S) bonds by cyclooctadieneiridium pyridine-2-carboxylate and related compounds

Abstract The complexes [Ir(O 2 CArN)(1,5-cod)] ( 1 ), containing the chelating ligands O 2 CArN=pyridine-2-carboxylate (O 2 CPic), isoquinoline-1-carboxylate (O 2 CIsoq), quinoline-2-carboxylate (O 2 CQuin) and pyrazine-2-carboxylate (O 2 CPyraz) are readily prepared in good yield from [Ir 2 (μ-OMe) 2 (1,5-cod) 2 ] and NArCO 2 H. The 1 H-NMR spectra of these compounds show temperature-dependent changes that are interpreted in terms of an interaction with the solvent. With Ph 3 SnH, Ph 3 SiH and C 6 F 5 SH complexes 1 react to give [Ir(O 2 CArN)(H)(SnPh 3 )(1,5-cod)] ( 2 ), [Ir(O 2 CArN)(H)(SiPh 3 )(1,5-cod)] ( 3 ) and [Ir(O 2 CArN)(H)(SC 6 F 5 )(1,5-cod)] ( 4 ), the reaction with Ph 3 SiH being reversible.