Bimetallic Perthiocarbonate Complexes of Cobalt: Synthesis, Structure and Bonding.

The syntheses and structural elucidation of bimetallic thiolate complexes of early and late transition metals are described. Thermolysis of the bimetallic hydridoborate species [{Cp*CoPh}{µ-TePh}{µ-TeBH3-ĸ2Te,H}{Cp*Co}] (Cp* = ɳ5-C5Me5) (1) in the presence of CS2 afforded the bimetallic perthiocarbonate complex [(Cp*Co)2(µ-CS4-κ1S:κ2S')(µ-S2-κ2S″:κ1S‴)] (2) and the dithiolene complex [(Cp*Co)(µ-C3S5-κ1S,S'] (3). Complex 2 contains a four-membered metallaheterocycle (Co2S2) comprising a perthiocarbonate [CS4]2- unit and a disulfide [S2]2- unit, attached opposite to each other. Complex 2 was characterized by employing different multinuclear NMR, infrared spectroscopy, mass spectrometry, and single-crystal X-ray diffraction studies. Preliminary studies show that [Cp*VCl2]3 (4) with an intermediate generated from CS2 and [LiBH4·THF] yielded thiolate species, albeit different from the cobalt system. Furthermore, a computational analysis was performed to provide insight into the bonding of this bimetallic perthiocarbonate complex.

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 [BH3·THF] and the mercaptopyridine ligand. Thermolysis of 2-mercaptopyridine, in the presence of [BH3·THF], afforded a doubly base-stabilized diborane(4) species 1, [HB(µ-C5H4NS)]2, along with the formation of its isomeric species 2, [HB(µ-C5H4NS)]2, albeit in less yield. Based on the coordination of the boron with the mercaptopyridine ligand in 2 and its spectroscopic data, compound 2 has been designated as a borato-boronium species, in which the anionic borate and cationic boronium units are covalently bonded to each other. Furthermore, we have demonstrated the oxidative insertion of chalcogen atoms (S and Se) through the B-B bond of the base-stabilized diborane(4), 1, that yielded chalcogenido-diboron species, 3(S) and 4(Se).

Synthesis and Chemistry of Dihydridoborate Group 7 Metal Complexes with Varied N,E-Chelated Ligands (E = O, NH, or S).

Several dihydridoborate group 7 metal complexes have been synthesized and their structural aspects have been described from various N,S-, N,N-, and N,O-chelated borate species, such as Na[(H3B)mp] (mp = 2-mercaptopyridyl), Na[(H3B)amt] (amt = 2-amino-5-mercapto-1,3,4-thiadiazolyl), Na[(H3B)hp] (hp = 2-hydroxypyridyl), Na[(H2B)bap] (bap = bis(2-aminopyridyl)), and Na[(H2B)bdap] (bdap = bis(2,6-diaminopyridyl)). Room temperature photolysis of [M2(CO)10] (M = Mn or Re) with these borate species afforded dihydridoborate complexes [(CO)3M(µ-H)2BHL] 1-6 (1, M = Mn, L = mp; 2, M = Re, L = mp; 3, M = Mn, L = amt; 4, M = Mn, L = hp; 5, M = Mn, L = ap; 6, M = Mn, L = dap, ap = 2-aminopyridyl, dap = 2,6-diaminopyridyl). In complexes 1-3, the corresponding (H2BHL) units are coordinated to the metal centers through the (κ3-H,H,S) mode. However, in complexes 4 and 5 (or 6), the connection is via (κ3-H,H,O) and (κ3-H,H,N) modes of coordination, respectively. Complexes 1 and 5 underwent hydroboration reactions with terminal alkynes that yielded trans-hydroborated species [Mn(CO)3(µ-H)2(NC5H4E)B(PhC═CH2)] (7, E = S; 8, E = NH). Density functional theory (DFT) calculations have been carried out to investigate the electronic structures of these dihydridoborate species as well as the nature of bonding in them.

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

Treatment of [Cp*RuCl2 ]2 , 1, [(COD)IrCl]2 , 2 or [(p-cymene)RuCl2 ]2, 3 (Cp*=η5 -C5 Me5, COD= 1,5-cyclooctadiene and p-cymene=η6 -i PrC6 H4 Me) with heterocyclic borate ligands [Na[(H3 B)L], L1 and L2 (L1 : L=amt, L2 : 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 L1 and L2 afforded dihydridoborate species [LA M(µ-H)2 BHL] 4-6 (4: LA =Cp*, M=Ru, L=amt; 5: LA =Cp*, M=Ru, L=mp; 6: LA =COD, M=Ir, L=mp). On the other hand, treatment of 3 with L2 yielded cis- and trans-bis(dihydridoborate) species, [Ru{(µ-H)2 BH(mp)}2 ], cis-7 and trans-7. The isolation and structural characterization of fac- and mer-[Ru{(µ-H)2 BH(mp)}{(µ-H)BH(mp)2 }], 8 from the same reaction offered an insight into the behaviour of these dihydridoborate species in solution. Fascinatingly, despite having reduced natural charges on Ru centres both at cis-and trans-7, they underwent hydroboration reaction with alkynes that yielded both Markovnikov and anti-Markovnikov addition products, 10 a-d.