Hydrolysis and Transfer Reactivity of the Coordinated Thiolate, Thiocarboxylate, and Selenolate in Binuclear Zinc(II) Complexes

Abstract

A new binuclear Zn­(II) complex, [Zn2(PhBIMP)­(DMF)2]3+ (1) (where PhBIMP1 is the anion of 2,6-bis­[bis­[(N-1-methyl-4,5-diphenylimidazoylmethyl)­amino]­methyl]-4-methylphenol), has been shown for the first time to mediate the hydrolytic C–S bond cleavage of a series of aliphatic and aromatic thiolates to yield the corresponding alcohols/phenols along with the formation of a hydrosulfide-bridged complex, [Zn2(PhBIMP)­(μ-SH)­(DMF)]2+ (2), which has been thoroughly characterized in comparison with the corresponding chloride complex, [Zn2(PhBIMP)­(Cl)­(DMF)]2+ (3), as a control. The binuclear Zn­(II)-thiolate complexes [Zn2(PhBIMP)­(μ-SR)]2+ (R = Ph, 4a; 3-Br-C6H4, 4b) have also been synthesized by avoiding the C–S bond cleavage reaction. Based on the experimental results for the effects of H2O and Et3N on 1, 4a, and 4b, the complex [Zn2(PhBIMP)­(μ-SR)­(OH)]1+ has been proposed to be the active intermediate that precedes the C–S bond cleavage of thiolates. The complex [Zn2(PhBIMP)­(μ-SCOPh)­(DMF)]2+ (5) also demonstrates the hydrolysis of the coordinated thiobenzoate to produce [Zn2(PhBIMP)­(μ-O2CPh)­(MeCN)]2+ (6). However, unlike 4a and 5, the benzeneselenolate-bridged complex, [Zn2(PhBIMP)­(μ-SePh)]2+ (7), does not generate the species, [Zn2(PhBIMP)­(μ-SePh)­(OH)]1+, in solution, and in line with that, the coordinated benzeneselenolate in 7 does not undergo hydrolysis to generate hydroselenide and phenol. Finally, a comparative study for the transfer reactivity of the bridging –SH, –SPh, –SC­(O)­Ph, and –SePh ligands in 2, 4a, 5, and 7, respectively, toward selected organic substrates has been performed to reveal the distinct differences in the reactivity of these bridging ligands.

Nonheme binuclear transition metal complexes with hydrosulfide and polychalcogenides

“…232 The Zn( ii )–SH distances in 8 (featuring a bridging hydrosulfide) again showed one short and one long Zn–SH distance of 2.3380(13) Å and 2.7802(13) Å, respectively, and a ∠Zn–(μ-SH)–Zn angle of 82.71(4)°. 235 However, unlike the general observation of one short and one long metal–hydrosulfide bond distance in the hydrosulfide bridged complexes ( Type C ), 7 featured nearly identical Ni( ii )–SH distances of 2.3813(15) Å and 2.3861(14) Å and a ∠Ni( ii )–(μ-SH)–Ni( ii ) angle of 83.76(5)°. 234 The ν SH for the binuclear transition metal–hydrosulfido complexes ranged from 2493–2560 cm −1 , which is similar to the ν SH values reported previously for other transition metal–hydrosulfido complexes, 6 while the S 2p binding energy ranged from 161.2–163.1 eV.…”

“…For example, N -Et-HPTB 1− provided only Type A complexes for both Fe( ii ) 231 and Co( ii ); 230 BPMP 1− provided only a Type B complex for Fe( ii ), 232 both Type B and Type C complexes for Co( ii ) 233 and only a Type C complex for Ni( ii ); 234 while PhBIMP 1− provided only Type C complexes for Fe( ii ), 232 Co( ii ) 233 and Zn( ii ). 235…”

“…A comparative study revealed that the ease of transfer of the coordinated HS − in 8 was comparable with the transfer of coordinated thiolate and selenolate in the corresponding thiolate and selenolate complexes, [Zn 2 (PhBIMP)(μ-EPh)] 2+ (E = S, Se), respectively. 235 Such a facile transfer of the coordinated HS − unit thus showed that while binuclear transition metal–hydrosulfide complexes can be synthesized by the hydrolysis of thiols, the resulting complexes can again be treated with suitable organic substrates to regenerate thiol functionality. A detailed comparative study involving the transfer of the coordinated hydrosulfide unit in the series of 12 complexes involving different metals, however, remains to be studied.…”

Transition Metal Mediated Hydrolysis of C–S Bonds: An Overview of a New Reaction Strategy

“…While on one hand thiolate/thiocarboxylate bridged Zn(II) complexes of the type [Zn 2 (PhBIMP)(μ-SR)](BF 4 ) 2 (R = Ph, 9a(BF 4 ) 2 ; 3−Br-C 6 H 4 , 9b(BF 4 ) 2 , C(O)Ph, 9c(BF 4 ) 2 ) could be isolated and characterized, a series of aliphatic and aromatic thiolates could also be hydrolyzed to generate the corresponding alcohols/ phenols (Scheme 5). 128 Reaction of a binuclear Zn(II)solvento complex, [Zn 2 (PhBIMP)(DMF) 2 ](BF 4 ) 3 (9d(BF 4 ) 3 ), with NaSCH 2 Ph in the presence of H 2 O and Et 3 N allowed the isolation of the binuclear Zn(II)-hydrosulfide compound, [Zn 2 (PhBIMP)(μ-SH)(DMF)](BF 4 ) 2 (9e(BF 4 ) 2 ), in 78% yield, along with the formation of PhCH 2 OH in 94% yield. The role of H 2 O (hydrolysis) was further confirmed by using H 2 18 O which led to the generation of 9e(BF 4 ) 2 and PhCH 2 18 OH in 77% and 90% yields, respectively.…”

Generation and Reactivity of Polychalcogenide Chains in Binuclear Cobalt(II) Complexes

“…Some important examples include the active sites of nitrogenases, − [Fe–Fe]-hydrogenase, − [NiFe]-hydrogenase, , sulfite reductase, − aconitase, − A and C cluster of [NiFe]-CODH, − [MoCu]-carbon monoxide dehydrogenase (CODH), − and bifunctional CODH/acetyl Co-A synthase (ACS). , The presence of these active sites provide proof for intriguing structures and offer formidable challenges to synthetic inorganic chemists. Combination of all these factors has immensely helped in the development of the chemistry of transition metals with hydrosulfides − and sulfides. ,,, …”