The interaction of Lewis acidic boron derivatives with Re(CO)5−nH(PMe3)n complexes

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.

Technetium(I) Carbonyl Chemistry with Small Inorganic Ligands

[Tc(OH₂)(CO)₃(PPh₃)₂](BF₄) has been used as a synthon for reactions with small inorganic ligands with relevance for the treatment of nuclear waste solutions such as nitrate, nitrite, pseudohalides, permetalates (M = Mn, Tc, Re), and BH₄^-. The formation of bond isomers and/or a distinct reactivity has been observed for most of the products. [Tc(NCO)(CO)₃(PPh₃)₂], [Tc(NCS)(CO)₃(PPh₃)₂], [Tc(CN)(CO)₃(PPh₃)₂], [Tc(N₃)(CO)₃(PPh₃)₂], [Tc(NCO)(OH₂)(CO)₂(PPh₃)₂], [Tc(η²-OON)(CO)₂(PPh₃)₂], [Tc(η¹-NO₂)(CO)₃(PPh₃)₂], [Tc(η²-OONO)(CO)₂(PPh₃)₂], [Tc(η¹-ONO₂)(CO)₃(PPh₃)₂], [Tc(η²-OO(CCH₃))(CO)₂(PPh₃)₂], [Tc(η²-SSC(SCH₃))(CO)₂(PPh₃)₂], [Tc(η²-SSC(OCH₃))(CO)₂(PPh₃)₂], [Tc(η²-SSC(CH₃))(CO)₂(PPh₃)₂], [Tc(η²-SS(CH))(CO)₂(PPh₃)₂], [Tc(OTcO₃)(acetone)(CO)₂(PPh₃)₂], [Tc(OTcO₃)(CO)₃(PPh₃)₂], and [Tc(η²-HHBH₂)(CO)₂(PPh₃)₂] have been isolated in crystalline form and studied by X-ray crystallography. Additionally, the typical reactivity patterns (isomerization, thermal decomposition, hydrolysis, or decarbonylation) of the products have been studied by spectroscopic methods. ⁹⁹Tc NMR spectroscopy has proved to be a particularly useful tool for the evaluation of such reactions of the diamagnetic technetium(I) compounds in solution.

Synthesis and structures of anionic rhenium polyhydride complexes of boron-hydride ligands and their application in catalysis

The rhenium complex, [K(DME)(18-c-6)][ReH₄(Bpin)(η²-HBpin)(κ²-H₂Bpin)] 1, comprising hydride and boron ligands only, has been synthesized by exhaustive deoxygenation of the commercially available perrhenate anion (ReO₄ ^-) with pinacol borane (HBpin). The structure of 1 was analysed by X-ray crystallography, NMR spectroscopy, and DFT calculations. While no hydrides were located in the X-ray crystal structure, it revealed a trigonal arrangement of pinacol boron ligands. Variable-temperature NMR spectroscopy supported the presence of seven hydride ligands but further insight was hindered by the fluxionality of both hydride and boron ligands at low temperature. Further evaluation of the structure by Ab Initio Random Structure Searching (AIRSS) identified the presence of hydride, boryl, σ-borane, and dihydroborate ligands. This complex, either isolated or prepared in situ, is a catalyst for the 1,4-hydroboration of N-heteroaromatic substrates under simple operating procedures. It also acts as a reagent for the stoichiometric C-H borylation of toluene, displaying high meta regioselectivity in the borylated products. Reaction of 1 with 9-BBN resulted in HBpin substitution to form the new anionic tetra(dihydroborate) complex [K(DME)(18-c-6)][Re(κ²-H-9-BBN)₄] 4 for which the hydride positions were clearly identified by X-ray crystallography. The method used to generate these isolable yet reactive boron-hydride complexes is direct and straightforward and has potential utility for the exploitation of other metal oxo compounds in operationally simple catalytic reactions.

Reactions of [(dmpe)2MnH(C2H4)]: synthesis and characterization of manganese(i) borohydride and hydride complexes

Reactions of trans-[(dmpe)₂MnH(C₂H₄)] (1) with BH₃(NMe₃), 9-BBN, and HBMes₂ yielded the manganese(i) borohydride complexes [(dmpe)₂Mn(μ-H)₂BR₂] (3: R = H, 4: R₂ = C₈H₁₄, 5: R = Mes). The reaction of 1 with BH₃(NMe₃) proceeds via ethylene substitution. By contrast, a detuerium labelling study indicates that the reaction of 1 with HBMes₂ involves initial isomerization of 1 to an unobserved 5-coordinate ethyl intermediate, [(dmpe)₂MnEt], which reacts with the hydroborane to afford EtBR₂ and [(dmpe)₂MnH], followed by reaction with a second equivalent of hydroborane to generate 5 (an analogous pathway is likely followed for other base-free hydroboranes such as 9-BBN). Identification of 3-5 as κ²-borohydride complexes, as opposed to boryl dihydride or hydroborane hydride isomers, is supported by ¹¹B NMR spectroscopy, X-ray diffraction, and Atoms in Molecules calculations. Two byproducts were observed in the syntheses of 3-5: [{(dmpe)₂MnH}₂(μ-dmpe)] (6) and [(dmpe)₂MnH(κ¹-dmpe)] (7). These complexes were independently prepared by exposure of 1 to free dmpe under an atmosphere of Ar or H₂, and the generality of this synthetic route was demonstrated by the reaction of 1 with PMe₃ (under H₂) to form [(dmpe)₂MnH(PMe₃)] (8). Complexes 6-8 can exist as isomers with either a trans or a cis relationship between the hydride and κ¹-coordinated phosphine ligands on manganese. trans to cis isomerization of 6-8 is photochemically induced, whereas the reverse reaction occurs under thermal conditions. X-ray crystal structures were obtained for 3-5, trans,trans-6, cis,cis-6, trans-7, and trans-8.