Antiaromatic compounds and small cyclic alkynes or carbynes are both challenging for synthetic chemists because of the destabilization caused by their antiaromaticity and highly distorted triple bonds, respectively. These dual destabilizations could be the reason why pentalyne (I), a highly antiaromatic and extremely strained cyclic alkyne, has never been synthesized.
Metallaaromatics have attracted continuing interest of both theoretical and experimental chemists since the first metallabenzene was predicted by Hoffmann and isolated by Roper. In sharp contrast to metallabenzenes, metallaphosphabenzene (MPB) is much less developed and has not been synthesized so far. Thus, developing synthetic approaches is urgent. Here we present thorough density functional theory (DFT) calculations on the thermodynamics and kinetics of the rearrangement between MPBs and the corresponding η5-phosphacyclopentadiene (η5-PCp) complexes.
Metallaaromatics have attracted considerable interest of both theoretical and experimental chemists. However, there have been only two metallanaphthalynes isolated so far. Thus, developing new synthetic approaches is urgent. Here we present thorough density functional theory (DFT) calculations on the thermodynamics and kinetics of the isomerization between metallanaphthalynes and metal indenylidene complexes. The effects of metal centers, ligands, and substituents on the metallabicycles were examined systematically.
Treatment of [PdI(Ph)(PPh3)]2 with allenes CH2═C═CHR (R = CMe3, CO2Et, P(O)(OEt)2, and SO2Ph) in dichloromethane at room temperature produces a mixture of cis and trans isomers of the π-allyl palladium complexes PdI(η3-CH2C(Ph)CHR)(PPh3) in which the R group is anti to the Ph group. The disubstituted allenes MeCH═C═CHR (R = P(O)(OEt)2 and SO2Ph) similarly react with [PdI(Ph)(PPh3)]2 to give the π-allyl palladium complexes PdI(η3-MeCHC(Ph)CHR)(PPh3) in which the R group is anti and the Me group is syn to the Ph group.
Treatment of RuHCl(CO)(PPh3)(3) with CH2=C=CHCO2Me gives the allyl complex Ru(77 3 -CH2CHCHCO2Me)CI(CO)(PPh3)(2). The analogous allyl complexes Os(eta(3)-CH2CHCHR)Cl(CO)(PPh3)(2) (R = Ph, CH2Ph) are also produced from the reactions of OsHCI(CO)(PPh3)(3) with CH2=C=CHR. In contrast, MHCl(PPh3)(3) (M = Ru, Os) react with CH2=C=CHR to give the vinyl complexes MCl((C(CH3)=CHR)(CH2 C=CHR)(PPh3)(2) (M = Ru, R = CMe3, M = Os, R = CMe3, Ph, CO2Et).
The nonplanarity found in metallabenzene complexes has been investigated theoretically via density functional theory (DFT) calculations. A metallabenzene has four occupied π molecular orbitals (8 π electrons) instead of three that benzene has. Our electronic structure analyses show that the extra occupied π molecular orbital, which is the highest occupied molecular orbital (HOMO) in many metallabenzenes, has antibonding interactions between the metal center and the metal-bonded ring-carbon atoms, providing the electronic driving force toward nonplanarity.
Reactions of CpW(CO)(2)(mu-PPh2)Mo(CO)(5) (1) with alkyl disulfides RSSR (R = Me, Et, Pr, Bu-n) in refluxing dichloromethane yielded the series of new mixed-metal and mixed-ligand bridged compounds CpW(CO)(mu-SR)(2)(mu-PPh2)Mo(CO)(3) (R = Me (4a), Et (4b), Pr (4c), Bun (4d)), CpW(CO)(mu-SR)2(mu-PPh2)Mo(CO)(mu-SR)(2) (R = Me (5a), Et (5b), Pr (5c), Bu-n (5d)), and CpW(CO)(mu-SR)(2)(mu-PPh2) Mo(CO)(2)(PPh2SR) (R = Me (6a), Et (6b), Pr (6c), Bu-n (6d)). All except 6c were characterized by single-crystal X-ray diffraction analysis.
Formal [2+2+2] addition reactions of the NBD ligand in [Cp*Ru(H2O)(NBD)]BF4 (NBD = norbornadiene) with H-2, Ph3SiH, ArCH=C=CH2, and RC=-CPh were observed. In contrast, olefins such as styrene and NBD do not undergo similar [2+2+2] addition reactions with [Cp*Ru(H2O)(NBD)]BF4. [Cp*Ru(H2O)(NBD)]BF4 reacts with H-2 in benzene to give [Cp*Ru(eta(6)-C6H6)]BF4 and nortricyclene. Similarly, [Cp*Ru(H2O)(NBD)]BF4 reacts with Ph3SiH to give [Cp*Ru(eta(6)-C6H5SiPh2OH)]BF4 and nortricyclene.
In this paper, the mechanism of alkyne metathesis catalyzed by W/Mo alkylidyne complexes has been theoretically investigated with the aid of density functional theory calculations. Calculations on various model alkylidyne complexes M( CMe)(OR)(3) (M = W, Mo; R = Me, CH2F), W( CMe)(NMe2)(3), and W( CMe)(Cl)(3) allow us to examine the factors that influence the reaction barriers. In the reaction mechanism, metallacyclobutadienes are initially formed from a ring-closing step between alkynes and alkylidyne complexes. A ring-opening step then gives the metathesis products.
Treatment of OsHCl(PPh3)(3) with allenes CH2=C=CHR at room temperature in benzene produced the vinyl complexes OsCl(C(CH3)=CHR)(CH2=C=CHR)-(PPh3)(2), instead of eta(3)-allyl complexes as normally observed. DFT calculations show that the formation of the vinyl complex is favored kinetically.