Vitaly A. Roznyatovsky

Regioselective synthesis of π-complexes of substituted polycyclic aromatic compounds. Experimental (NMR) and theoretical (DFT) studies of η6,η6-haptotropic rearrangements in naphthalenechromiumtricarbonyl complexes☆

A new regioselective method for the synthesis of (η6-naphthalene)chromium tricarbonyl complexes bearing a substituent R in desired positions of either the coordinated or non-coordinated ring was proposed. The kinetics of η6,η6-haptotropic rearrangements (IRHR) was investigated by NMR spectroscopy for ten pairs of isomer complexes (R=D, CH3, Me3Sn, Me3Si and Cl in position 1 or 2 of coordinated or non-coordinated rings). The free activation energies ΔG# fall into a quite narrow range of 28–31 kcal mol−1 and are therefore relatively insensitive to the influence of substituent R whereas equilibrium constants of IRHR change considerably from 0.03 to 17.26 within the compounds investigated. Electron donating (withdrawing) substituents R increase (decrease) the relative thermodynamic stability of the isomers containing a substituent in coordinated rings. The density functional theory method (DFT) with extensive basis set describes quite satisfactory the geometry and the energy of ground states and correctly predict that the least motion route of Cr(CO)3 from one ring to another via the center of the C4a–C8a bond is forbidden. The transition state for the rearrangement of (η6-naphthalene)chromium tricarbonyl has trimethylenemethane structure of C2v-symmetry in which the Cr(CO)3-group is slightly shifted to the ligand periphery. For the monosubstituted naphthalenechromium tricarbonyls thus, there are two reaction channels of the chromium tricarbonyl group slippage between unsubstituted and substituted rings, one of which is practically unperturbed determining the low sensitivity of the rearrangement rate to the effects of ligand substitution even for 1-R substituted complexes. Calculated activation barriers are in a good accordance with the experimentally determined ΔG# values.

Ricochet inter-ring haptotropic rearrangement of σ-methyl-(η5-indenyl) chromium tricarbonyls. Experimental kinetic and theoretical DFT study

Abstract σ -Methyl-( η 5 -indenyl) chromium tricarbonyl ( III ) rearranges quantitatively into η 6 -1-endo-methylindene) chromium tricarbonyl ( IV ) in C 6 D 6 solution at 30–60°C. Methyl group attachment to the positions 2 or 3 of indenyl ligand in ( III ) has no influence on the activation parameters of this ricochet inter-ring haptotropic rearrangement ( ΔG # =23.6 kcal mol −1 ; ΔH # =18.9±0.2 kcal mol −1 ; ΔS # =−18.6±0.2 cal K −1 mol −1 ). ( IV ) undergoes further irreversible isomerization at 60–120° into ( ν 6 -3-methylindene) chromium tricarbonyl ( V ) with a higher activation barrier ( ΔG # =28.5±0.1 kcal mol −1 ) via two consecutive [1,5]-sigmatropic hydrogen shifts. The mechanisms of both rearrangements have been studied in detail using density functional theory (DFT) calculations with extended basis sets. Calculations show that the rearrangement ( III ) → ( IV ) proceeds in two steps. Methyl group migration from chromium into position 1 of the indenyl ligand is the rate-determining step leading to the formation of the 16-electron intermediate ( VII ). The calculated activation barrier ( E a =19.6 kcal mol −1 ) is in good agreement with the experimental one. Further rearrangement ( VII ) → ( V ) proceeds via a trimethylenemethane-type transition state ( XVIII ) with an activation barrier 11.8 kcal mol −1 . The coordination of the chromium tricarbonyl group at the six-membered ring has only minor influence on the kinetic parameters of the hydrogen [1,5]-sigmatropic shift in indene.

Stereochemical nonrigidity of the square complex (PPh3)2Pt(HgGePh3)(GePh3)

Abstract 31P, 195Pt and 199Hg NMR spectra of complex (PPh3)2Pt(HgGePh3)(GePh3) (I) have been studied. The spectra at temperatures below −40°C prove that (I) is a cis-isomer with the square-planar coordination of the Pt atom. The reversibility of temperature dependences of spectra, insensitivity of line shape to the solvent, concentration and presence of free phosphine establish the fluxional behaviour of (I). The activation parameters of the intramolecular rearrangement which is realized, most probably, through a digonal twist, are: Δ≠298 = 51.5 ± 2.9 kJ/mol, ΔH≠ = 59.3 ± 2.9 kJ/mol, ΔS≠ = 26.2 ± 9.7 J/mol. K.

1H NMR Spectra and electronic structure of binuclear niobocene and titanocene containing fulvalene ligands

1H NMR spectra of binuclear metallocene hydride complexes, (η5 : η5-C10H8)(C5H5)2M2(μ-H)2 (M = Nb, 20°C and Ti, (−60 to +25°C), were studied. The Nb complex is diamagnetic and gives a high resolution spectrum. The coordination of bridging hydride H atoms provides Nb atoms with complete 18 electron configuration. In its ground state, the Ti complex is also diamagnetic (the spectrum at −60°C agrees to that) in spite of only 17 electron configuration of each Ti atom. However, the population of the excited triplet state in the case of the Ti complex is appreciable at temperatures higher than −30°C, the proton resonance lines being shifted downfield and significantly broadened as compared with the spectrum at −60°C.

Controlled ring-opening polymerisation of cyclic phosphates, phosphonates and phosphoramidates catalysed by heteroleptic BHT-alkoxy magnesium complexes

We report here that the heteroleptic BHT-Mg(OR) complex, i.e. [(BHT)Mg(OBn)(THF)]2 (Mg3), represents an effective and versatile ring-opening polymerisation (ROP) catalyst for several cyclic ethylene phosphate monomers (CEPMs), such as ethylene phosphates with methoxy- (MeOEP, 1), isopropoxy- (iPrOEP, 2), and tert-butoxy- (tBuOEP, 3) substituents, N,N-diethyl ethylene phosphoramidate (Me2NEP, 4) as well as ethyl (EtPPn, 5) and tert-butyl (tBuPPn, 6) ethylene phosphonates. Mg3 retains its catalytic activity over a broad temperature range from −50 to 100 °C and efficiently carries out the fast and controlled polymerisation of CEPMs with sterically unhindered alkoxy groups with less than 1% chain branching even at near-complete conversion. Compared with ROP catalysed by 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), Mg3 performs much better in the polymerisation of CEPMs with bulky groups and of monomers sensitive to strong nucleophiles, such as tBuOEP.

symm-Tetramethylenecyclooctane: En Route to Polyspirocycles

A straightforward gram-scale synthesis of 1,3,5,7-tetrakis(methylidene)cyclooctane (TMCO) from commercial adamantane-1,3-dicarboxylic acid has been developed. TMCO exhibits high reactivity toward a number of carbenes and epoxidizing reagents, undergoing multiple cyclopropanations, dihalocyclopropanations, or epoxidations of four double bonds to yield polyspirocyclic products. Stereochemical features of polyspirocyclopropanated compounds have been thoroughly examined in experimental (NMR) and theoretical (DFT) studies. Comprehensive stereochemical assignment of TMCO adducts with dihalocarbenes and spiroepoxy products was achieved. The conditions of the formation of 1-methyl-3,7-bis(methylidene)bicyclo[3.3.1]nonane from the adamantane derivative were optimized, and diadducts of this diene with dihalocarbenes were isolated and characterized.

Quantitative 2H NMR spectroscopy. 1. Thermodynamic H/D isotope effects in N,N-dimethylformamide and cyclopentadiene molecules

A new method for quantification of the relative distribution of deuterium in molecules is proposed. The technique is based on the lineshape analysis in the 2H NMR spectra obtained at the natural abundance level of deuterium with allowance for inhomogeneity of the magnetic field. The equilibrium thermodynamic H/D isotope effects for hindered rotation about the C—N bond in the N,N-dimethylformamide molecule and for prototropic exchange in the cyclopentadiene molecule were determined. The results obtained agree with those of DFT calculations of the vibrational energies.

Beyond the Dimer and Trimer: Tetraspiro[2.1.25.1.29.1.213.13] hexadecane‐1,3,5,7‐tetraone—the Cyclic Tetramer of Carbonylcyclopropane

Tetraspiro[2.1.2(5).1.2(9).1.2(13).1(3)]hexadecane-1,3,5,7-tetraone 4, a unique tetraketone containing a cyclooctane core and four spiroannelated cyclopropane moieties, represents the previously unknown cyclotetramer of carbonylcyclopropane. For this purpose oxidation of the parent polyspirocyclic hydrocarbon was examined under various oxidative conditions, and the reactivity of oxidants towards methylene groups of the eight-membered cycle, activated by adjacent spirocyclopropane rings, was evaluated and contrasted. Whereas the treatment of tetraspirohexadecane with ozone resulted in monooxidation, its reaction with methyl(trifluoromethyl)dioxirane afforded the product of four-fold oxidation, triketoalcohol 10. Subsequent oxidation of the latter with Dess-Martin periodinane gave the target tetraketone 4.

Tricarbonylchromium complexes with phenalene. Synthesis, structure, and thermal rearrangements

The reaction of phenalene with Cr(CO)3Py3/BF3·OEt2 afforded a mixture of two isomeric complexes, tricarbonyl(6a,7-9,9a,9b-·6-phenalene)chromium (1) and tricarbonyl(3a,6a,9b,4-6-·6-phenalene)chromium (2). Deprotonation of the mixture of compounds1 and2 followed by treatment with MeI, BunI, or D2O gave complexesexo-1-R-1 (3–5: R=Me (3), Bun (4), or D (5)). The molecular geometry of complex3 was established by X-ray structural analysis. Heating of complex5 in toluene or C6F6 at 90–110 °C resulted in redistribution of deuterium among positionsexo-1,endo-1, and 3 in the resulting complexes of types1 and2via sigmatropic shifts of the Hexo and Hendo atoms in the nonaromatic ring as well asvia inter-ring migrations of the tricarbonylchromium group. In the case of3, the methyl label is distributed among positionsexo-1 and3 to form isomeric complexes with similar structures (exo-1-Me-2 (6), 3-Me-2 (7), and 3-Me-1 (8), respectively)via processes analogous to those observed in the case of isomerization of compound5 (except for migration of the Hexo atom). The mechanisms of these rearrangements are discussed.

CCDC 1843930: Experimental Crystal Structure Determination

Related Article: Olga N. Gorunova, Ivan M. Novitskiy, Yuri K. Grishin, Igor P. Gloriozov, Vitaly A. Roznyatovsky, Victor N. Khrustalev, Konstantin A. Kochetkov, Valery V. Dunina|2018|Organometallics|||doi:10.1021/acs.organomet.8b00363