Ekaterina V. Bakhmutova

Crown Compounds for Anions: Sandwich and Half-Sandwich Complexes of Cyclic Trimeric Perfluoro-o-phenylenemercury with Polyhedralcloso-[B10H10]2− andcloso-[B12H12]2− Anions

It has been shown by IR and NMR spectroscopy that cyclic trimeric perfluoro-o-phenylenemercury (o-C6F4-Hg)3 (1) is capable of binding closo-[B10H10]2- and closo-[B12H12]2- anions to form complexes [[(o-C6F4Hg)3](B10-H10)]2- (2), [[(o-C6F4Hg)3]2(B10H10)]2-(3), [[(o-C6F4Hg)3](B12H12)]2- (4), and [[(o-C6F4Hg)3]2(B12H12)]2- (5). According to IR data, the bonding of the [B10H10]2- and [B12H12]2- ions to the macrocycle in these complexes is accomplished through the formation of B-H-Hg bridges. Complexes 2, 3, and 5 have been isolated in analytically pure form and have been characterized by spectroscopic means. X-ray diffraction studies of 3 and 5 have revealed that these compounds have unusual sandwich structures, in which the polyhedral di-anion is located between the planes of two molecules of 1 and is bonded to each of them through two types of B-H-Hg bridges. One type is the simultaneous coordination of a B-H group to all three Hg atoms of the macrocycle. The other type is the coordination of a B-H group to a single Hg atom of the cycle. According to X-ray diffraction data, complex 2 has an analogous but half-sandwich structure. The obtained complexes 2-5 are quite stable; their stability constants in THF/acetone (1:1) at 20 degrees C have been determined as 1.0 x 10(2)Lmol(-1), 2.6 x 10(3)L(2)mol(2), 0.7 x 10(2)Lmol(-1), and 0.98 x 10(3)L(2)mol(-2), respectively.

In situ IR and NMR study of the interactions between proton donors and the Re(I) hydride complex [{MeC(CH2PPh2)3}Re (CO)2H]. ReH…H bonding and proton-transfer pathways

Abstract The reactions of various proton donors (phenol, hexafluoro-2-propanol, perfluoro-2-methyl-2-propanol, monochloroacetic acid, and tetrafluoroboric acid) with the rhenium (I) hydride complex [(triphos)Re(CO)2H] (1) have been studied in dichloromethane solution by in situ IR and NMR spectroscopy. The proton donors from [(triphos)Re(CO)2H…HOR] adducts exhibiting rather strong H…H interactions. The enthalpy variations associated with the formation of the H-bonds (−ΔH = 4.4–6.0 kcal mol−1) have been determined by IR spectroscopy, while the H…H distance in the adduct [(triphos)Re(CO)2H…HOC(CF3)3] (1.83 A) has been calculated by NMR spectroscopy through the determination of the T1min relaxation time of the ReH proton. It has been shown that the [(triphos)Re(CO)2H…HOR] adducts are in equilibrium with the dihydrogen complex [(triphos)Re(CO)2(η2-H2)]+, which is thermodynamically more stable than any H-bond adduct.

Dihydrogen bonding of decahydro-closo-decaborate(2−) and dodecahydro-closo-dodecaborate(2−) anions with proton donors: experimental and theoretical investigation

Abstract The interactions of [Bu 4 N] 2 [B 10 H 10 ] and [Bu 4 N] 2 [B 12 H 12 ] with various proton donors (MeOH, EtOH, Pr i OH, PhOH, 4-FC 6 H 4 OH, 4-NO 2 C 6 H 4 OH, CF 3 CH 2 OH, (CF 3 ) 2 CHOH, (CF 3 ) 3 COH) in low polarity media were investigated. The site of coordination for [B 10 H 10 ] 2− and [B 12 H 12 ] 2− was found to be hydride hydrogen. Spectral (IR, NMR) evidences for the BH⋯HO hydrogen bonding between the boron hydrides and the OH proton donors in solution are presented. Spectral (Δ ν , Δ ν 1/2 , ΔA) and thermodynamic (Δ H °, Δ S °) characteristics of the H-complexes were determined. The BH⋯HO bonding strength increases from [B 12 H 12 ] 2− to [B 10 H 10 ] 2− . The geometry, energy, as well as electron distribution in the [B 10 H 10 ] 2− ·HOCH 3 , [B 10 H 10 ] 2− ·HOCF 3 , [B 10 H 10 ] 2− ·HCN, and [B 12 H 12 ] 2− ·HOCH 3 complexes were studied using ab initio HF/6-31G approximation. It was shown that increase of the proton donor ability of acids leads to formation of bifurcate H-bonds.

Problems of unusual hydrogen bonds between proton donors and transition metal hydrides and borohydrides

The results of experimental and theoretical studies of intermolecular MH...HX and BH...HX hydrogen bonds with the hydride hydrogen atom acting as a proton accepting site are analyzed. Spectral (IR and NMR) criteria for their formation are presented. The spectral, structural, and thermodynamic characteristics of these unusual hydrogen bonds obey the regularities found for classical hydrogen bonds. It was shown that the MH...HX bonds participate in the proton transfer with the formation of nonclassical cationic hydrides and the |M(η2-H2|+ hydrogen bonds are formed in low-polarity media. Problems arising in this new line of investigations are discussed.

Crown compounds for anions. Spectroscopic and theoretical studies of complexation of borohydride anions with cyclic trimeric perfluoro-o-phenylenemercury

It has been shown by IR and NMR spectroscopy that cyclic trimeric perfluoro-o-phenylenemercury (o-C6F4Hg)3 (1) is capable of binding borohydride anions in THF and 1,2-dichloroethane solutions to form complexes {[(o-C6F4Hg)3](BH4)2}2− (2) and {[(o-C6F4Hg)3]2(BH4)}− (3). According to the IR data, complex 2 contains both terminal and coordinated B–H bonds while all four B–H bonds of the BH4− ion are coordinated with the mercury atoms in complex 3. The use of NMR spectroscopy provided the identification of one more complex of 1 with BH4−, which can be formulated as {[(o-C6F4Hg)3](BH4)}− (4). The stability constants of complexes 2 and 3 have been determined by IR spectroscopy. Quantum-chemical calculations of 2–4 by the AM1 method suggest that the complexes have the unusual bipyramidal, sandwich and half-sandwich structures, respectively. In contrast to 1, the interaction of (C6F5)2Hg with BH4− anions in THF gives a single complex {[(C6F5)2Hg](BH4)}− (5) independently of the reagent ratio. This complex is much less stable than 2 and 3.

REACTIONS OF CARBONYLMETALLATE ANIONS WITH 1-HALOALKYNES

The main regularities of the reactions of 1-haloalkynes RC≡CX with carbonylmetallate anions [(η5-C5R′5)(CO)3M]− (R′ = H (1–3),, M=Cr (1), M=Mo (2), or M=W (3); R′ =Me (4–6), M=Cr (4), M=Mo (5), or M=W (6) were revealed. It was established that the first stage of the reactions of anions1–6 with bromo- or iodoalkynes RC≡CX (X=Br or I) involved the transfer of the halogen atom from the sp-hybridized carbon atom to the transition metal atom to form carbonyl halides [(η5-C5R′5)(CO)3MX. To the contrary, the reactions of anions1–6 with chloroalkynes RC≡CCl proceeded selectively as a nucleophilic substitution at the unsaturated carbon atom, the reaction rate being governed by the nucleophilicity of the carbonylmetallate anions and the electron-withdrawing ability of the R group. These reaction paths are consistent with the structures of the lowest unoccupied molecular orbitals (LUMO) in the PhC≡CX molecules (X=Cl, Br, or I) calculated by the MNDO/PM3 method. In the case of the reactions of 1-chloroheptyne-1 C1C≡CC5H11n, anions1–3 appeared to be insufficiently nucleophilic, but these reactions can be performed as cross-coupling of the carbonylmetallate anions with chloroalkynes catalyzed by palladium complexes.