Synthesis of Alkyl- and Aryl[hydrotris(pyrazolyl)borato]carbonylruthenium Complexes by Decarbonylation of Alcohols. Synthesis of TpRuH(H₂)(PPh₃) [Tp = Hydrotris(pyrazolyl)borate], an Observable Intermediate in the Decarbonylation Reaction

Abstract

Treatment of TpRuCl(PPh 3 )(CH 3 CN) (Tp ) hydrotris(pyrazolyl)borate) with NaBH 4 in ethanol did not yield the expected hydride complex TpRuH(PPh 3 )(CH 3 CN) (2) but rather the methyl carbonyl complex TpRu(CH 3 )(CO)(PPh 3 ) (1b). Formation of 1b was due to decarbonylation of ethanol by 2 generated in situ by NaBH 4 reduction of TpRuCl(PPh 3 )(CH 3 -CN). Analogous reactions in the presence of other primary alcohols RCH 2 OH (R ) H, C 2 H 5 , n-C 3 H 7 , C 6 H 5 , C 6 H 4 CH 3 -4, and C 6 H 4 Cl-4) led to the corresponding σ-organyl complexes TpRuR(CO)(PPh 3 ). A common feature of the reactions is that the R groups of alcohols RCH 2 -OH become the σ-organyl groups in the final metal complexes. A mechanism involving metal-η 2 -aldehyde and -η 2 -dihydrogen intermediates is proposed for the decarbonylation reaction. This is supported by the observation of the η 2 -dihydrogen complex TpRuH(H 2 )-(PPh 3 ) (3) during the decarbonylation reaction. 3 was synthesized independently by heating a THF solution of 2 under 40 atm of H 2 at 60 °C for 48 h or by heating 2 in CH 3 OH at 60 °C under 6 atm of H 2 for 5-6 h.

Ruthenium‐Catalyzed β‐Alkylation of Secondary Alcohols with Primary Alcohols

“…Aryl methyl carbinols can be alkylated with many primary alcohols. The reactions with benzyl alcohols and heterocyclic alcohols (entries 2-7) give higher conversions than with primary aliphatic alcohols (entries [8][9][10][11][12]. The lowering of the conversion in alkylation reactions with primary alkyl alcohols is not attributable to selfcondensation of these alcohols because no self-condensation products were detected in the reactions; it is probably due to diminished electrophilicity of the carbonyl carbon atoms of the aldehydes generated via oxidation of the primary alkyl alcohols.…”

“…Formation of the phenyl carbonyl complexes M8 and M10 is probably due to benzaldehyde decarbonylation at the metal center. We have previously reported that the complex TpRu-A C H T U N G T R E N N U N G (PPh 3 )(CO)Ph (M10) can be prepared by reacting TpRuA C H T U N G T R E N N U N G (PPh 3 )A C H T U N G T R E N N U N G (CH 3 CN)H with benzaldehyde; [9] the Cp analogue M8 is independently prepared in this study. Decarbonylation of aldehydes by transition metal complexes to form carbonyl complexes is well-established.…”

Ruthenium‐Catalyzed Hydrogenation of Carbon Dioxide to Formic Acid in Alcohols

“…A doublet of doublets (J H,P ϭ 26.4, J C,H ϭ 9.3 Hz) is observed in the upfield region at δ ϭ Ϫ11.81 ppm, which can be assigned to the carbonyl hydride complex TpRu(PPh 3 )(CO)H (3), which we have previously reported. [7] The 31 P{ 1 H} spectrum exhibits a major singlet at δ ϭ 52.9 ppm, which is due to 2. A singlet at δ ϭ 66.1 ppm is assignable to 3, while the singlet at δ ϭ 30.9 ppm is identified as the signal of triphenylphosphane oxide, which was probably formed by CO 2 oxidation of PPh 3 .…”

“…In our previous work, highpressure NMR spectroscopy monitoring of the catalytic CO 2 hydrogenation with 1 in hydrous THF revealed that the carbonyl hydride complex 3 was the major rutheniumcontaining species after prolonged heating at 100°C. Moreover, in the course of the reaction, a very small amount of TpRu(PPh 3 )(H 2 )H (4) [7] (4) with formic acid and the dihydrogen hydride species was present in such low concentration that it eluded detection by NMR spectroscopy. Examples relevant to the formation of 3 can be found in the literature.…”

Half-sandwich trihydrido ruthenium complexes

“…By contrast, a family of permethyl substituted complexes Cp * (R 3 P)RuH 3 (Cp * @C 5 Me 5 ) is well described [15], including the X-ray structure of Cp * (Ph 3 P)RuH 3 [16]. Complex 1a is a classical trihydride [16], whereas the isolobal tris(pyrazolyl)borate complex Tp(Ph 3 P)RuH(g 2 -H 2 ) exist in a hydride(dihydrogen) form [17], underpinning the strong effect of the ring on the extent of Ru-H interaction. Here, we report facile general access to a series of complexes Cp(R 3 P)RuH 3 (R 3 P@Ph 3 P (a), Ph 2 Pr i P (b), PhPr i 2 P (c) and Pr i 3 P (d)) and the crystal structure of complex Cp(Ph 2 Pr i P)RuH 3 .…”