Ring Expansion versus exo−endo Isomerization in (2-Pyridyl)methylenecyclobutane Coordinated to Hydrido(trispyrazolyl)borate- and Cyclopentadienyl-Osmium Complexes

Abstract

The reactions of (2-pyridyl)methylenecyclobutane with the metal fragments [OsTp(P i Pr 3 )] þ and [OsCp(P i Pr 3 )] þ (Tp = hydridotris(pyrazolyl)borate, Cp = cyclopentadienyl) are shown. Complex [OsTp(κ 1 -OCMe 2 ) 2 (P i Pr 3 )]BF 4 (1) reacts with the organic substrate to give 3) as a result of the ring expansion of the methylenecyclobutane unit of the coordinated substrate. The reaction of (2-pyridyl)methylenecyclobutane with [OsCp(NCCH 3 ) 2 (P i Pr 3 )]PF 6 (4) leads to [À N}-(P i Pr 3 )]PF 6 (5). In contrast to 2, complex 5 evolves by means of exo-endo isomerization of the C-C double bond of the coordinated substrate to afford [ À OsCp{η 2j C(dCHCH 2 C j H 2 )-CH 2 -C 5 H 4 À N}(P i Pr 3 )]PF 6 (6).

Osmium Models of Intermediates Involved in Catalytic Reactions of Alkylidenecyclopropanes

“…The formation of complex 2 is in agreement with the previous result using the triisopropylphosphine complex [OsCp­(CH 3 CN) 2 (P i Pr 3 )]­PF 6 and most probably arises from the initial coordination of the nitrogen atom and the C–C double bond of the substrate to the osmium atom of 1 , which leads to intermediate C (Scheme ) . The subsequent oxidation of the metal center promotes sp 2 to sp 3 rehybridizations of the nitrogen atom and the C­(sp 2 ) atom of the three-membered ring to afford the 1-osma-2-azacyclopent-3-ene intermediate D .…”

“…The geometry around the metal center is close to octahedral with the Cp ligand occupying one of the faces. The metal coordination sphere is completed by the phosphorus atom of the phosphine ligand and the chelate 2-pyridylcyclobutene molecule, which coordinates through the nitrogen atom and the C(6)–C(7) double bond with Os–N­(1), Os–C(6), and Os–C(7) distances of 2.105(9), 2.306(17) and 2.114(16) Å, respectively . The 1 H and 13 C­{ 1 H} NMR spectra of 3 are consistent with the structure shown in Figure .…”

Reactions of an Osmium Bis(dihydrogen) Complex under Ethylene: Phosphine Addition to a C–C Double Bond and C–H Bond Activation of Fluoroarenes

“…7 Thus, in contrast to the dihydride dihydrogen Cp cation [OsH 2 Cp(η 2 -H 2 )(P i Pr 3 )] + , 8 the Tp counterpart [OsTp(η 2 -H 2 ) 2 (P i Pr 3 )]BF 4 (1) is a rare example of a bis(dihydrogen) derivative that does not contain any hydride coligand. 6 This bis(dihydrogen) compound is the starting point of an interesting novel organometallic OsTp chemistry with unsaturated organic molecules (Scheme 1), including the transformation of terminal alkynes into carbynes and carbenes, 9 the olefin−alkylidene tautomerization of 2-vinylpyridine, 10 the formation of cyclobutylidene 11 and cyclopentylidene 12 derivatives by ring expansion of pyridyl-substituted alkylidenecyclopropanes and alkylidenecyclobutanes, the cleavage of both C(sp 3 )−C(sp 2 ) bonds of alkylidenecyclopropanes in the absence of a coordinating substituent, 13 and the double C−H bond activation of gem-disubstituted allenes to afford hydride alkenylcarbyne species. 14 Now, we report the formation of a phosphoniumethyl ligand and the C−H bond activation of fluoroarenes.…”

Syntheses, structures and electrochemical properties of homoleptic ruthenium(III) and osmium(III) complexes bearing two tris(carbene)borate ligands

“…It is surprising that no ruthenium and osmium complex with the Ph[B(R-ImH) 3 ] ligand has been reported yet. In comparison, the chemistry of Ru and Os complexes with tris(pyrazolyl)borate (Tp) ligand (C, Chart 1) has been extensively studied [27][28][29][30][31][32][33][34].Herein we report the synthesis, structure, X-ray photoelectronic spectroscopy (XPS), and electrochemical properties of ruthenium(III) and osmium(III) complexes [PhB(ImMe) 3 ] 2 M(OTf) (M = Ru, 1a; M = Os, 1b) with two tris(carbene)borate ligands. To our knowledge, 1b is the first Os(III)-NHC complex and 1a is among a limited number of Ru(III)-NHC complexes reported in the literature [35].…”

“…It is surprising that no ruthenium and osmium complex with the Ph[B(R-ImH) 3 ] ligand has been reported yet. In comparison, the chemistry of Ru and Os complexes with tris(pyrazolyl)borate (Tp) ligand (C, Chart 1) has been extensively studied [27][28][29][30][31][32][33][34].…”