Properties and Reactivities of the Hydrido Ligands in Iridium Sulfido Clusters Relevant to Activation and Production of H₂

Abstract

Sulfido-hydrido clusters whose cores consist of three to six iridium atoms, [(Cp*Ir) 3 (µ 3 -S)(µ 2 -H) 3 ][BF 4 ] (2), [(Cp*Ir) 4 (µ 3 -S) 2 (µ 2 -H) 3 ][BF 4 ] (3), [(Cp*IrH) 2 (Cp*Ir)(µ 3 -S)(µ 2 -H) 2 ], [(Cp*IrH) 4 (µ 4 -S)(µ 2 -H) 2 ], and [(Cp*Ir) 5 Ir(µ 3 -S) 5 H], were isolated from the reactions of [(Cp*Ir) 2 (µ 2 -H) 3 ][BF 4 ] (Cp* ) η 5 -C 5 Me 5 ) with NaSH in MeOH. Treatment of 2 with KOBu t afforded the deprotonated product [(Cp*Ir) 3 (µ 3 -S)(µ-H) 2 ] (7), which was protonated by HBF 4 to give 2 reversibly. Addition of HBF 4 to 3 formed the dicationic cluster [(Cp*Ir) 4 (µ 3 -S) 2 (µ-H) 2 ][BF 4 ] 2 (10) with concurrent evolution of H 2 , which was converted back to 3 under H 2 atmosphere in the presence of excess pyridine at 50 °C. In contrast, reactions of 10 with H 2 conducted in the presence of various alkylamines at 20-50 °C afforded the mixtures of 3 and its stereoisomer 11. Conversion of 10 into 3 was also achieved by the reaction with 2 equiv of Cp 2 Co in the presence of [Et 3 NH][BF 4 ], which furnished the cycle of reducing H + into H 2 mediated by the Ir 4 S 2 cluster. Cluster 10 readily reacted with CO (1 atm) at 20 °C to give [(Cp*Ir) 4 (µ 3 -S) 2 (µ-H) 2 (CO)][BF 4 ] 2 ( 13), where the CO ligand was bound in an end-on fashion to one of the two Ir centers connected to two µ 3 -sulfido ligands. Analogous adduct formation was observed in the reaction of 10 with 1 equiv of XyNC (Xy ) 2,6-dimethylphenyl), yielding two stereoisomers of [(Cp*Ir) 4 (µ 3 -S) 2 (µ-H) 2 (CNXy)][BF 4 ] 2 , one of which was the analogue of 13 and the other had the XyNC ligand coordinating to the same Ir site but with the inverted orientation around the metal. On the other hand, treatment of 10 with excess N 2 H 4 gave the hydrazine cluster [(Cp*Ir) 4 (µ 3 -S) 2 (µ 2 -H) 2 (N 2 H 4 ) 2 ][BF 4 ] 2 , in which two terminal hydrazine ligands were bonded to one of two Ir sites supported by only one µ 3 -sulfido ligand. On the basis of these findings about the adduct formations, reaction pathways of 10 with H 2 in the presence of bases are discussed. Structures of all new clusters reported here were determined by spectroscopic methods and, except for 7, by X-ray crystallography.

Ruthenium Complexes for Catalytic Dehydrogenation of Hydrazine and Transfer Hydrogenation Reactions

“…Seino and Mizobe et al. also reported a ( η 5 ‐C 5 Me 5 )Ir coordinated bis‐hydrazine cluster [{( η 5 ‐C 5 Me 5 )Ir} 4 ( μ 3 ‐S) 2 ( μ 2 ‐H) 2 (N 2 H 4 ) 2 ] 2+ having two hydrazine molecules coordinated to a single ( η 5 ‐C 5 Me 5 )Ir moiety connected through the bridging sulphur of the Ir 3 cluster . Analogously, several Ru‐hydrazine complexes were also reported, which upon oxidation may form corresponding diazene species,– such as, Ru‐hydrazine [RuH(N 2 H 4) L 4 ] + and Ru–bis‐hydrazine complexes [Ru(N 2 H 4 ) 2 L 4 ] 2+ (L=P(OEt) 3 , PPh(OEt) 2 , P(OMe) 3 resulted in the formation of Ru‐diazene complexes upon treatment of Pb(OAc) 4 in DCM at −80 °C .…”

“…Hydrazine coordinated transition metal complexes have been receiving huge scientific attention because of the involvement of metal‐hydrazine species as important intermediates in several reactions of global importance including nitrogen to ammonia reduction . Therefore, such hydrazine coordinated complexes based on Fe, W, Mo, Ir, Ru and others have been extensively explored for diverse applications (Figure ) . For instance, Tyler et al.…”

H–H and N–H Bond Cleavage of Dihydrogen and Ammonia with a Bifunctional Parent Imido (NH)-Bridged Diiridium Complex

“…The four iridium atoms form a butterfly-type core with five Ir–Ir contacts ranging from 2.9097(4) to 2.9484(4) Å, suggesting delocalized metal–metal bonding interactions in the 64-electron cluster, for which only four metal–metal bonds would be expected on the basis of the effective atomic number rule. Although the hydrido ligands could not be located in the X-ray analysis, the 1 H NMR spectrum of 4 was consistent with an approximately C 2 v -symmetric structure with two μ 3 -bridging hydrido ligands, as in the isoelectronic sulfido clusters . The broad signal due to the NH protons at δ 2.87 disappeared upon treatment with D 2 O.…”

Binuclear cyclopentadienyliridium hydride chemistry: Terminal versus bridging hydride and cyclopentadienyl ligands

“…The terminal ν(Ir-H) frequencies were found to range from 2098 to 2282 cm -1 , which lie within the established range of 1800 to 2500 cm -1 . 6,36,37 The bridging ν(Ir-H) frequencies are much lower, ranging from 1372 to 1684 cm -1 . The experimental ν(Ir-H) frequencies of the pentamethylcyclopentadienyl deriviatives, measured in KBr pellets, exhibit the same trend but are 100 to 200 cm -1 below the predicted ν(Ir-H) frequencies for their unsubstituted cyclopentadienyl analogues.…”