Richard H. Heyn

Preparation and reactivity of 16-electron ‘half-sandwich’ ruthenium complexes; X-ray crystal structure of (η5-C5Me5)Ru(PPri3)Cl

The new 16-electron ruthenium compounds (η5-C5Me5)Ru(L)Cl [(1), L = PPri3; (2), L = PCy3](Cy = cyclohexyl) were prepared from [(η5-C5Me5)RuCl]4 and PPri3 or PCy3, respectively, and the X-ray crystal structure of (1) has been determined; reactions of the title compounds with CO, C2H4, pyridine, and PhSiH3 are described.

A gold exchange: a mechanistic study of a reversible, formal ethylene insertion into a gold(III)-oxygen bond.

The Au(III) complex Au(OAc(F))2(tpy) (1, OAc(F) = OCOCF3; tpy = 2-p-tolylpyridine) undergoes reversible dissociation of the OAc(F) ligand trans to C, as seen by (19)F NMR. In dichloromethane or trifluoroacetic acid (TFA), the reaction between 1 and ethylene produces Au(OAc(F))(CH2CH2OAc(F))(tpy) (2). The reaction is a formal insertion of the olefin into the Au-O bond trans to N. In TFA this reaction occurs in less than 5 min at ambient temperature, while 1 day is required in dichloromethane. In trifluoroethanol (TFE), Au(OAc(F))(CH2CH2OCH2CF3)(tpy) (3) is formed as the major product. Both 2 and 3 have been characterized by X-ray crystallography. In TFA/TFE mixtures, 2 and 3 are in equilibrium with a slight thermodynamic preference for 2 over 3. Exposure of 2 to ethylene-d4 in TFA caused exchange of ethylene-d4 for ethylene at room temperature. The reaction of 1 with cis-1,2-dideuterioethylene furnished Au(OAc(F))(threo-CHDCHDOAc(F))(tpy), consistent with an overall anti addition to ethylene. DFT(PBE0-D3) calculations indicate that the first step of the formal insertion is an associative substitution of the OAc(F) trans to N by ethylene. Addition of free (-)OAc(F) to coordinated ethylene furnishes 2. While substitution of OAc(F) by ethylene trans to C has a lower barrier, the kinetic and thermodynamic preference of 2 over the isomer with CH2CH2OAc(F) trans to C accounts for the selective formation of 2. The DFT calculations suggest that the higher reaction rates observed in TFA and TFE compared with CH2Cl2 arise from stabilization of the (-)OAc(F) anion lost during the first reaction step.

Microwave methods for the synthesis of gold(III) complexes

New microwave methods were developed for the synthesis of cationic and neutral gold(III) complexes. Six examples of [AuCl2(N–N)][PF6], containing 2,2′-bipyridine-type ligands, and three examples of AuCl2(C–N), containing cyclometallated 2-phenylpyridine-type ligands, were successfully prepared. Two of the complexes, [AuCl2(5,5′-dimethyl-2,2′-bipyridine)][PF6] and [AuCl2(4,4′,5,5′-tetramethyl-2,2′-bipyridine)][PF6], have not been previously reported. Generally, the microwave-heated reactions gave analytically pure products within minutes – a substantial improvement over conventional procedures. In conjunction, the thermal stabilities of some of the complexes were studied by thermogravimetric analysis. The transformation of AuCl3(2-(p-tolyl)pyridine) into its cyclometallated analog AuCl2(tpy), marked by the loss of a mass corresponding to HCl, was observed.

Synthesis and structure of [(η5-C5Me5Ru(μ-NHPh)]2,an electron-deficient ruthenium amide complex

Abstract The reaction of [Cp*Ru(μ3-Cl]4 (Cp* = η5-C5Me5) with NaNHPh in THF affords the blue anilide complex [Cp*Ru(μ-NHPh)]2. Characterization of this complex by X-ray crystallography reveals a folded dimeric structure with bridging anilide ligands.

SYNTHETIC, STRUCTURAL AND REACTIVITY STUDIES WITH NEW GROUP 4 TRANSITION-METAL SILYL COMPLEXES

Abstract The silyl chloride complexes (η5-C5H4SiMe3)Zr[Si(SiMe3)3]Cl (1) and Cp2M[SiMe3)3]Cl (M = Ti (2); Zr (3); Hf (4)) were prepared by reaction of the appropriate metallocene dichloride with a silyl lithium reagent. The X-ray crystal structures of 1 and 3 are described. Methylation of 1, 3, and 4 with Grignard reagents afford (η5-C5H4SiMe3)2Zr[Si(SiMe3) 3]Me (5) and Cp2M[Si(SnMe3)3]Me ( M = Zr ( 6 ); Hf ( 7 ) ). Complex 1 is a catalyst for the dehydropolymerization of both PhSiH3 and nBu2SnH2 to relatively low molecular weight polymers. Whereas 3 and 4 do not react with carbon monoxide, 2 undergoes CO-induced reductive elimination to Cp2Ti(CO)2 and ClSi(SnMe3)3.

Ruthenium(IV) silyl hydride complexes via reaction of silanes with 16-electron [Ru(η5-C5Me5)(PPri3)X](X = Cl, CH2SiHPh2, SiMePh2) complexes. Hydride migrations to an η2-silene ligand

Reactions of [Ru(η5-C5Me5)(PPri3)(H)(η2-CH2SiPh2)] with hydrosilanes occur via initial migration of hydride to the silene ligand, and eventually give disilyl hydride or silyl dihydride ruthenium(IV) complexes; the 16-electron chloride[Ru(η5-C5Me5)(PPri3)Cl] adds mesityl (Mes) silane to give [Ru(η5-C5Me5)(PPri3)(H)2(SiHcMes)] which was crystallographically characterized.

Structural and spectroscopic characterization of potassium fluoroborohydrides

Mechanochemical reactions between KBH4 and KBF4 result in the formation of potassium fluoroborohydrides K(BH(x)F(4-x)) (x = 0-4), as determined by (11)B and (19)F solid state NMR. The materials maintain the cubic KBH4 structure. Thermogravimetric (TG) data for a ball-milled sample with KBH4 : KBF4 = 3 : 1 are consistent with only desorption of hydrogen.

Semi‐Batch Polymerisations of Ethylene with Metallocene Catalysts in the Presence of Hydrogen, 3. Correlation Between Hydrogen Sensitivity and Molecular Parameters

Semi-batch ethylene polymerisations have been carried out with heterogenised Cp 2 ZrCl 2 /MAO, Ind 2 ZrCl 2 /MAO, Cp(Ind)ZrCl 2 /MAO and Cp(Flu)ZrCl 2 / MAO (MAO, methylaluminoxane) catalysts where hydrogen was added as the chain-transfer agent. Modelling of molecular weight distributions of the polymer formed gave estimates of the relative rate constant for the chain transfer to hydrogen and the rate constant for propagation, k tH2 /k p . Values of 0.7(2), 22(7), 13(3) and 35(4) were obtained for the Cp 2 , Ind 2 , (Cp,Ind) and (Cp,Flu) catalysts, respectively. The observed order of reactivity towards hydrogen has been correlated with chemical shifts from 91 Zr NMR and with the atomic charges of zirconium from DFT calculations for a series of metallocene complexes, The efficiency of hydrogen as a chain-transfer agent is larger the more electron deficient the zirconium atom in the catalyst is.

Synthesis of Aromatic Carbamates from CO2: Implications for the Polyurethane Industry

Abstract Polyurethanes are ubiquitous polymers that have wide ranging applications and are present in many of the products we use on a daily basis. An entire industry has developed over many years to exploit the inherent versatility of these materials, and major capital investments continue to be made in the production of the chemical components. For the isocyanates, conversion of primary amines by reaction with phosgene has become established as the normal synthesis method, but research aimed at avoiding use of this toxic chemical continues. Replacement of phosgene with CO 2 to make intermediate carbamate polymers is one alternative. This chapter will consider the potential of this chemistry by providing a brief introduction to the polyurethane industry and then the current and potential use of CO 2 in polyurethane production. Thereafter, various alternative routes to carbamates are discussed, followed by a description of the state-of-the-art technology for the synthesis of aromatic carbamates from aniline, CO 2 , and an alcohol. The thermodynamics of this reaction requires removal of the coproduced water to increase carbamate yields, and the investigation herein has utilized ionic liquids (ILs) as potential water-sequestering cosolvents. This empirical study has utilized a high-throughput batch-scale reactor to screen a large number of ILs and potential catalysts. Three catalyst/IL combinations, which provide higher selectivity for carbamate than for the in situ -produced precursor diphenylurea, have been identified. One of these combinations has been scaled up and provides the first example of one-pot synthesis of an aromatic carbamate from aniline, CO 2 , and an alcohol.

Influence of nanoconfinement on morphology and dehydrogenation of the Li11BD4–Mg(11BD4)2 system

The decomposition of a nanoconfined mixture of lithium-magnesium borohydride, Li(11)BD(4)-Mg((11)BD(4))(2), has been investigated and compared to the corresponding mixture in the bulk form. The systems were investigated by thermal analysis, small-angle neutron scattering, (11)B nuclear magnetic resonance and transmission electron microscopy. The dehydrogenation temperatures decreased by up to 60 °C in the nanoconfined system, with gas evolution following different steps, compared to the behaviour of the bulk material under the same conditions. Most importantly, desorption from the nanoconfined hydride proceeds without formation of diborane, B(2)D(6), which evolves from the bulk mixture. From small-angle neutron scattering, differences in morphology between the bulk and the nanoconfined systems are also demonstrated. Evidence of a complete decomposition has been found in the nanoconfined system, after heating up to 460 °C. Furthermore, (11)B NMR data show that nanoconfinement inhibits the formation of dodecaborane, [B(12)D(12)](2-), during decomposition, a result which is important for practical applications of borohydrides.