Regioselective Reactions of 1,3-Diynes with the Titanocene Vinylidene Fragment [Cp*₂TiCCH₂]. Crystal and Molecular Structure of Cp*₂TiC(C⋮CSiMe₃)C(SiMe₃)CCH₂

Abstract

The titanocene vinylidene intermediate [Cp*2TiCCH2] (6) (Cp*: C5(CH3)5), formed by ethene or methane elimination from Cp*2TiCH2CH2CCH2 (5) and Cp*2Ti(CHCH2)(CH3) (7), respectively, reacts with 1,3-diynes RC⋮C-C⋮CR (R = Me (13a), Ph (13b), SiMe3 (13c), CMe3 (13d)) by a [2 + 2]-cycloaddition, giving metallacyclobutenes Cp*2TiC(C⋮CR)CRCCH2 (9a−d). Using the unsymmetrical 1,3-diyne RC⋮CC⋮CR1 (R = CMe3, R1 = SiMe3 (13e)), a 9:1 mixture of the metallacyclobutenes Cp*2TiC(C⋮CR)CR1CCH2 (9e) and Cp*2TiC(C⋮CR1)CRCCH2 (9e‘) is formed. In all cases, exclusive formation of one regioisomer exhibiting the C⋮CR substituent in the α-position of the metallacycle is observed. The regioselectivity of the formation of 9 is attributed to the polarity of the C⋮C bond as well as the stereochemical conditions, proven by ab initio calculations at the Hartree−Fock (HF) level of theory with the 3-21G(*) standard basis set and molecular modeling. The X-ray structure of 9c is presented. Subsequent reactions of 9 with an excess of the titanocene intermediate 6, to form binuclear metallacycles, are not observed.

Insertion of Terminal and Internal Acetylenes into the Zr−μ-Methylene Bond of the Dinuclear Cationic Zirconium Complex [{Zr(η5-C5H5)}2(μ-CH2)(μ-Cl)(μ-η5-C5H4-η5-C5H4)][BMe(C6F5)3]. Synthetic Aspects, NMR Spectroscopic Study, and Dynamic Behavior in Solution

“…Consequently the subsequent methylene 1,2-addition for the silyl acetylene A2 takes place, while a 2,1-addition is favored for the alkyl acetylenes B2 , in which the chlorine bridge is broken, and in both cases a bridging three-carbon chain and a cationic Zr(1) center is formed. Mononuclear titanocene vinylidene intermediates react with alkynes 15 or 1,3-diynes with insertion into the TiC double bond to give planar titanacyclobutenes. Similarly, A2 may form a planar “ Zr(2) − C(SiMe 3 )C  CHCD 2 ” unit with the μ-propene ligand resulting from insertion of the alkyne into a Zr−C single bond of the μ-methylene ligand in the dinuclear fulvalene complex 1D .…”

Preparation of Osmium η3-Allenylcarbene Complexes and Their Uses for the Syntheses of Osmabenzyne Complexes

“…The η 1 -allenylcarbene complexes Cp­(CO)­(NO)­WC­(NEt 2 )­C­(R)CHCMe 3 (R = Me, Et) were isolated from the reactions of Cp­(CO)­(NO)­WCCHCMe 3 with the electron-rich alkynes RCCNEt 2 . The metallacyclobutene complexes RuCl­{C­(COOMe)CHC­[CH­(C 6 H 4 Me)]}­{P­(C 6 H 4 Me) 3 } 2 (NO) and Cp* 2 Ti­{C­(R)C­(R)­CCH 2 } were isolated from the reactions of alkynes with RuCl­{CCH­(C 6 H 4 Me)]}­{P­(C 6 H 4 Me) 3 } 2 (NO) and Cp* 2 TiCCH 2 , respectively. η 3 -Allenylcarbene complexes [CpRu­(C­(R′)-η 2 -CHCCHR′)­(PR 3 )]­PF 6 (R′ = ferrocenyl, R = Ph, Cy; R′ = ruthenocenyl, R = Ph), [CpOs­{CPh-η 2 -CHCCHPh}­(P i Pr 3 )]­BF 4 , and CpReBr 2 {C­(SCH 2 Ph)-C­(CH 2 Ph)C­(SCH 2 Ph)C­(SCH 2 Ph) 2 } were isolated from the reactions of [RuCp­(PR 3 )­(CH 3 CN) 2 ]­PF 6 with ferrocenyl/ruthenocenyl acetylenes, the reaction of the dihydride dihydrogen complex [CpOsH 2 (η 2 -H 2 )­(P i Pr 3 )]­BF 4 with phenylacetylene, and the reaction of the η 2 -alkyne complex CpReBr 2 (η 2 -PhCH 2 SCCSCH 2 Ph) with PhCH 2 SCCSCH 2 Ph, respectively.…”

1,3-Metal–Carbon Bonding Predicts Rich Chemistry at the Edges of Aromatic Hydrocarbons

“…The Laplacian analysis suggests that metallacycles with M−C β distances significantly shorter than the sum of the covalent radii of M and C may show 1,3-MC bonding. Hence, RAJXIJ, RAJXOP, WOFYAS, PAXJON, WOFZOH, and WOFGED are examples of "edge complexes" with unmistakable 1,3-MC interactions, while the RAQXIQ, 27 ZUXHEF, 28 LIKRAY, 20 IQOMEG, and LOSQUF are borderline cases.…”