Abstract
The ruthenium-zinc heterobimetallic complexes, [Ru(IPr)2(CO)ZnMe][BArF4] (7), [Ru(IBiox6)2(CO)(THF)ZnMe][BArF4] (12) and [Ru(IMes)'(PPh3)(CO)ZnMe] (15), have been prepared by reaction of ZnMe2 with the ruthenium N-heterocyclic carbene complexes [Ru(IPr)2(CO)H][BArF4] (1), [Ru(IBiox6)2(CO)(THF)H][BArF4] (11) and [Ru(IMes)(PPh3)(CO)HCl] respectively. 7 shows clean reactivity towards H2, yielding [Ru(IPr)2(CO)(η2-H2)(H)2ZnMe][BArF4] (8), which undergoes loss of the coordinated dihydrogen ligand upon application of vacuum to form [Ru(IPr)2(CO)(H)2ZnMe][BArF4] (9). In contrast, addition of H2 to 12 gave only a mixture of products. The tetramethyl IBiox complex [Ru(IBioxMe4)2(CO)(THF)H][BArF4] (14) failed to give any isolable Ru-Zn containing species upon reaction with ZnMe2. The cyclometallated NHC complex [Ru(IMes)'(PPh3)(CO)ZnMe] (15) added H2 across the Ru-Zn bond both in solution and in the solid-state to afford [Ru(IMes)'(PPh3)(CO)(H)2ZnMe] (17), with retention of the cyclometallation.
Highlights
Heterobimetallic complexes featuring a transition metal (TM) in partnership with a Lewis acidic (LA), typically main group element, have been the focus of considerable interest[1] because of their potential to bring about the cooperative activation of E–H (E = H, N, Si etc.) bonds.[2]
We reported that addition of GaMe3, InMe3 and ZnEt2 to the bulky N-heterocyclic carbene (NHC) stabilised cationic ruthenium hydride complex [Ru(IPr)2(CO)H][BArF4] (1; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene; BArF4 = [B{C6H3(3,5-CF3)2}4]−)[5] resulted in alkane elimination and formation of the Ru–Ga, Ru–In and Ru–Zn complexes 2–4 shown in Scheme 1.6 Of most relevance to this current paper was the ruthenium–zinc complex [Ru(IPr)2(CO)ZnEt][BArF4] (4) which, upon treatment with H2, both coordinated dihydrogen at Ru and added H2 across the Ru–Zn bond to give [Ru(IPr)2(CO)(η2-H2) (H)2ZnEt][BArF4] (5)
In an effort to test whether a cationic (NHC)Ru hydride precursor was necessary, we examined the reaction of the neutral precursor [Ru(IMes)(PPh3)(CO)
Summary
The tetramethyl IBiox complex [Ru(IBioxMe4)2(CO)(THF)H][BArF4] (14) failed to give any isolable Ru–Zn containing species upon reaction with ZnMe2. There was no reaction between 1 and ZnPh2 (even upon heating to 70 °C) presumably due to the unfavourable combination of bulky substituents on the NHC and Zn. Upon exposure of a fluorobenzene solution of 7 to 1 atm H2, an instantaneous change in colour from red-orange to colourless was observed, resulting from the formation of the dihydrogen dihydride complex, [Ru(IPr)2(CO)(η2-H2)(H)2ZnMe] [BArF4] (8, Scheme 2).[11] This showed less fluxional behavior than the ZnEt analogue 5, exhibiting three low frequency hydride signals (δ −5.15, −7.83 and −12.16 in a 2 : 1 : 1 ratio) at room temperature compared to just two resonances for 5
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