Reactions of a Dihydrogen Complex with Terminal Alkynes: Formation of Osmium−Carbyne and −Carbene Derivatives with the Hydridotris(pyrazolyl)borate Ligand

Abstract

The dihydrogen complex [OsTp(η 2 -H 2 )(κ 1 -OCMe 2 )(P i Pr 3 )]BF 4 (1; Tp ) hydridotris(pyrazolyl)borate) reacts with tert-butylacetylene to give the hydride-carbyne derivative [OsHTp(tCCH 2 t Bu)(P i Pr 3 )]BF 4 (2). Similarly, the treatment of 1 with (trimethylsilyl)acetylene in the presence of methanol leads to [OsHTp(tCCH 3 )(P i Pr 3 )]BF 4 (3). In chloroform at 60 °C, complexes 2 and 3 evolve into the corresponding chloro derivatives [OsClTp(tCR)(P i Pr 3 )]BF 4 (R ) CH 2 t Bu (4), CH 3 ( 5)), whereas in acetonitrile the carbenes [OsTp(dCHR)(NCCH 3 )(P i Pr 3 )]BF 4 (R ) CH 2 t Bu (6), CH 3 ( 7)) are formed. Complex 1 also reacts with phenylacetylene. The reaction initially gives [OsHTp(tCCH 2 Ph)(P i Pr 3 )]BF 4 (8). Subsequently, the insertion of a second molecule of alkyne into the Os-H bond of 8 and the migration of the resulting alkenyl group from the metal center to the carbyne carbon atom take place, to afford the carbene [OsTp{dC(CH 2 Ph)C(Ph)dCH 2 }(P i Pr 3 )]BF 4 (9). The metal center of 9 is saturated by means of a strong agostic interaction (r bp ) 0.4(1)) between the osmium atom and one of the ortho-CH bonds of the phenyl substituent of the alkenyl unit of the alkenylcarbene ligand. Treatment of 1 with methylpropiolate leads to the carbene [OsTp{dCHCH 2 C(O)OMe}(P i Pr 3 )]BF 4 (10) in a one-pot synthesis. Complexes 2, 4, 9, and 10 have been characterized by X-ray diffraction analysis. † Dedicated to Professor Jose ´Gimeno on the occasion of his 60th birthday.

A Cobalt(I) Pincer Complex with an η2‐Caryl−H Agostic Bond: Facile C−H Bond Cleavage through Deprotonation, Radical Abstraction, and Oxidative Addition

“…Theoverall geometry about the cobalt center is best described as distorted trigonal bipyramidal, where the two carbonyl ligands and the agostic h 2 -C aryl -H bond define the equatorial plane and the phosphine moieties the axial positions.T he bond between the ipso-carbon and the Co atom is extremely long (2.2197 (6) + (5)a re substantially shorter:1 .998(2) and 1.953-(2) , respectively.T he H(1) atom (which was located in difference Fourier maps and refined freely) strongly interacts with the cobalt center (1.72(2) ), which was also evident from the 1 HNMR spectrum of 3.I ti sn oteworthy that this hydrogen is severely removed from the aromatic plane by approximately 358 8 (in related Ru, Rh, and Os complexes,this angle is in the range of 14-30 o ). [5,7,10,14] TheC 1 ÀH1 bond length of 1.05(3) i si nt he range observed in X-ray diffraction measurements for unactivated hydrocarbons (for example,1.08 i nC 6 H 6 ).…”

The contrasting chemical reactivity of potent isoelectronic iminopyridine and azopyridine osmium(ii) arene anticancer complexes

“…The current work appears to be the first detection of an osmium(II) hydride NMR peak for an osmium hydride in an aqueous solution. [56][57][58][59][60][61][62][63][64] These findings suggest that osmium arene complexes can modulate the redox balance in cells by a novel mechanism. 95 1 H NMR studies show that complexes 6 and 14 are more effective in oxidising NADH than 8 and 16 after 24 h incubation at 310K ( Figure S5).…”

Osmium–carbon multiple bonds: Reduction and C–C coupling reactions

“…However, when the coligands contribute only to the electronic structure of the metal center, the difference in energy between the dihydride and dihydrogen tautomers seems to be the factor determining the formed product. Thus, dihydride complexes, which afford dihydrogen species by coordination of electron poor-Lewis bases, and dihydrogen compounds react with terminal alkynes, HC^CR, to give hydrideecarbyne derivatives [7], including OsHCl 2 (^CCH 2 R)(P i Pr 3 ) 2 [4a]. Alkenylcarbyne counterparts, OsHCl 2 {^CCR 0 ]CR 1 R 2 }(P i Pr 3 ) 2 , have been prepared by means of the reactions of the known dihydride starting complex OsH 2 Cl 2 (P i Pr 3 ) 2 (1) [8] with four different types of organic substrates: alkynols, allenes, enynes, and dienes.…”