A Pair of Dinuclear Fe(II) Enantiomers: Syntheses and Structures of ΛΔ/ΔΛ-Bis(Dihydridoborate) Complexes.

In our effort to establish a direct synthetic approach for bis(dihydridoborate) complexes of first-row transition metals, we have investigated the reactivity of [Cp*Fe(dppe)Cl] (dppe =1,2-bis(diphenylphosphino)ethane) with Na[BHL] (L =2-mercaptopyridine (mp) and 2-mercaptobenzothiazole (mbz)) that led to the formation of iron(II) dihydridoborate complexes, [Cp*Fe{κ-S,H,H-(HBH(L))}] 1 a-b (L=mp (1 a) and L=mbz (1 b)). Further, in an attempt to isolate the bis(dihydridoborate) complex of iron by the insertion of borane into the κ-N,S-chelated iron complex, [(dppe)Fe{κ-N,S-(mp)}] (2), we have isolated and structurally characterized a rare example of dimeric iron bis(dihydridoborate) complex, [Fe{κ-S,H,H-(HBH(mp))}], ΛΔ/ΔΛ-3 as pair of enantiomers. Interestingly, these enantiomers ΛΔ/ΔΛ-3 have two trans-[Fe{κ-S,H,H-(HBH(mp))}] moieties bridged through sulfur atoms of 2-mercaptopyridinyl ligands, where the iron centres are hepta-coordinated.

Quantifying variation in cooperative B-H bond activations using Os(ii) and Os(iii) κ-,-chelated complexes: same, but different.

In an effort to investigate small molecule activation by heavier transition metal (TM) based κ-,-chelated species, we have synthesised a series of bis-κ-1,3-,-chelated complexes of osmium, [Os(PPh)(κ-,-L/L)], 2a-b, and [Os(PPh)(L/L)(κ-,-L/L)], 3a-b (2a and 3a: L[double bond, length as m-dash] = CHNS; 2b and 3b: L = CHNS), from the thermolysis of [Os(PPh)Cl], 1, with a potassium salt of heterocyclic ligands L and L. The former complexes are diamagnetic in nature, while the EPR spectra, XPS study and density functional theory (DFT) calculations have substantiated the paramagnetic behaviour of 3a-b with a significant spin contribution from non-innocent ligands. These species were engaged in B-H activation of boranes utilizing the combined effect of hemilability and metal-ligand cooperativity (MLC), where 2a-b upon treatment with BH·SMe yielded Os(σ-borate)hydride complexes, [Os(PPh)(H){κ-,,'-BH(L/L)}], 4a-b (4a: L = CHNS; 4b: L = CHNS).

Doubly Base-Stabilized Diborane(4) and Borato-Boronium Species and Their Chemistry with Chalcogens.

In an effort to isolate diborane(4) derivatives, we have developed an efficient and uncatalyzed approach using [BH·THF] and the mercaptopyridine ligand. Thermolysis of 2-mercaptopyridine, in the presence of [BH·THF], afforded a doubly base-stabilized diborane(4) species , [HB(μ-CHNS)], along with the formation of its isomeric species , [HB(μ-CHNS)], albeit in less yield. Based on the coordination of the boron with the mercaptopyridine ligand in and its spectroscopic data, compound has been designated as a borato-boronium species, in which the anionic borate and cationic boronium units are covalently bonded to each other.

B-P Coupling: Metal Stabilized Phosphinoborate Complexes.

In an effort to establish B-P coupling reactions without the use of phosphine-borane dehydrocoupling agent, we have developed a new synthetic methodology employing group 8 metal σ-borate complex [{κ -H,S,S'-BH L }Ru{κ -H,H,S-BH L}] (L=NC H S), 1. Treatment of 1 with chlorodiphenyl phosphine (PPh Cl) yielded 1,5-P,S chelated Ru-dihydridoborate species [PPh H{κ -H,H,S-BH(OH)L}Ru{κ -P,S-(Ph P)BH L}], 2. The insertion of phosphine moiety (PPh ) by the cleavage of 3c-2e σ(Ru H-B) bonding interaction led to the formation of B-P bond.

Coordination and Hydroboration of Ru(II)-Borate Complexes: Dihydridoborate vs. Bis(dihydridoborate).

Treatment of [Cp*RuCl ] , 1, [(COD)IrCl] , 2 or [(p-cymene)RuCl ] 3 (Cp*=η -C Me COD= 1,5-cyclooctadiene and p-cymene=η - PrC H Me) with heterocyclic borate ligands [Na[(H B)L], L and L (L : L=amt, L : L=mp; amt=2-amino-5-mercapto-1,3,4-thiadiazole, mp=2-mercaptopyridine) led to the formation of borate complexes having uncommon coordination. For example, complexes 1 and 2 on reaction with L and L afforded dihydridoborate species [L M(μ-H) BHL] 4-6 (4: L =Cp*, M=Ru, L=amt; 5: L =Cp*, M=Ru, L=mp; 6: L =COD, M=Ir, L=mp). On the other hand, treatment of 3 with L yielded cis- and trans-bis(dihydridoborate) species, [Ru{(μ-H) BH(mp)} ], cis-7 and trans-7.

Stabilization of dichalcogenide ligands in the coordination sphere of a ruthenium system.

The synthesis, structure and electronic properties of tetraruthenium dichalcogenide complexes displaying the exclusive coordination mode of dichalcogenide ligands have been discussed. The reactions of Li[BHE] (E = S or Se) with [ClRu(μ-Cl)(-cymene)] (-cymene = η-{-CH(Pr)Me}) at room temperature yielded tetrametallic dichalcogenide complexes [{RuCl(-cymene)}(μ,η-E)], 1-2 (E = S (1) and Se (2)). The solid-state X-ray structure of 1 shows that two {(-cymene)RuCl} moieties are bridged by a S-S bond.

Directed Syntheses of CS- and CS-Bridged Decaborane-14 Analogues.

To establish a procedure for single-cage cluster expansion of open cage dimetallaoctaboranes(12), we have investigated the chemistry of -[(Cp*M)BH] (η-CMe = Cp*, : M = Co; : M = Rh), with diverse chalcogen-based borate ligands. As a result, treatment of - and - with Li[BHE] (E = S, Se, or Te) yielded 10-vertex -[(Cp*Co)BEH] (: E = S; : E = Se; : E = Te) along with known 10-vertex -[(Cp*M)BHE] (: E = S, M = Co; : E = Se, M = Co; : E = Te, M = Co; : E = Se, M = Rh). The geometries of dimetallachalcogenaboranes, -, are isostructural with decaborane(14).