Preparation, Spectroscopic Characterization, X-ray Structure, and Theoretical Investigation of Hydride−, Dihydrogen−, and Acetone−OsTp Complexes:  A Hydridotris(pyrazolyl)borate−Cyclopentadienyl Comparison

Abstract

Complex OsH 3 Cl(P i Pr 3 ) 2 (1) reacts with KTp (Tp ) hydridotris(pyrazolyl)borate) in tetrahydrofuran at room temperature to give OsH 3 (κ 2 -Tp)(P i Pr 3 ) 2 (2). In toluene at 80 °C, the κ 2 -Tp complex 2 is transformed to the κ 3 -Tp derivative OsH 3 Tp(P i Pr 3 ) (3) in quantitative yield after 7 h. Protonation of 3 with HBF 4 affords the bis(dihydrogen) compound [OsTp(η 2 -H 2 ) 2 (P i Pr 3 )]BF 4 (4). In acetone complex 4 releases the coordinated hydrogen molecules in a sequential manner. At room temperature, the dihydrogensolvate complex [OsTp(η 2 -H 2 )(κ 1 -OCMe 2 )(P i Pr 3 )]BF 4 (5) is formed, while at 56 °C the loss of both hydrogen molecules gives rise to the bis-solvento derivative [OsTp(κ 1 -OCMe 2 ) 2 (P i Pr 3 )]BF 4 (6). Complexes 2-6 have been characterized by X-ray diffraction analysis, and DFT calculations support their formulation. The structures of 3-5 have been compared with those of their Cp counterparts OsH 3 Cp(P i Pr 3 ), [OsH 2 -Cp(η 2 -H 2 )(P i Pr 3 )]BF 4 , and [OsH 2 Cp(κ 1 -OCMe 2 )(P i Pr 3 )]BF 4 . The results show that the Tp ligand avoids piano stool geometries, while it enforces dispositions allowing N-Os-N angles close to 90°such as octahedron and pentagonal bipyramid.

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

“…Because the TpOs II L fragment shows a very low tendency to afford Os IV species by oxidative addition, ,,, the formation of 3 and 4 most probably involves a σ-bond metathesis reaction between the activated C–H bond of the arene and the Os–C bond in an Os(CH 2 CH 2 P i Pr 3 )(η 2 -CH-arene) intermediate, which is generated by dissociation of an arm of the Tp ligand. In this context, it should be mentioned that an EXSY experiment under an ethylene atmosphere revealed no exchange between coordinated and free ethylene molecules.…”

“…With some notable exceptions, the majority of the bis(dihydrogen) compounds of late transition metals also contain hydride ligands . The hydridotris(pyrazolyl)borate ligand (Tp) avoids the piano-stool structures typical for the cyclopentadienyl group (Cp) and enforces dispositions allowing N–Os–N angles close to 90°. , These structures favor nonclassical interactions between the hydrogen atoms bonded to the metal center . Thus, in contrast to the dihydride dihydrogen Cp cation [OsH 2 Cp(η 2 -H 2 )(P i Pr 3 )] + , 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 …”

Anti-Markovnikov 1,3-CH Addition of Allenes to Allenes: A Straightforward Method To Prepare Osmium–Dienylcarbene Complexes

“…All reagents, with the exception of NaBAr F 4 (BAr F 4 = tetrakis­(3,5-bis­(trifluoromethyl)­phenyl)­borate), which was prepared as previously reported, were obtained from commercial sources and used without further purification. The starting material [OsTp­(κ 1 -OCMe 2 ) 2 (P i Pr 3 )]­BF 4 ( 1 ) was prepared according to the published method …”

Polyhydrides of Platinum Group Metals: Nonclassical Interactions and σ-Bond Activation Reactions

“…In toluene at 80 °C, this κ 2 -Tp complex is transformed to the κ 3 -Tp derivative OsH 3 (κ 3 -Tp)­(P i Pr 3 ) ( 428 ), in quantitative yield after 7 h, as a result of the dissociation of one of the phosphines and the coordination of the free pyrazolyl group of 427 (Scheme ). Protonation of 428 with HBF 4 ·OEt 2 in diethyl ether affords the bis­(dihydrogen) compound [OsTp­(η 2 -H 2 ) 2 (P i Pr 3 )]­BF 4 ( 429 ) . In acetone, complex 429 releases the coordinated hydrogen molecules in a sequential manner.…”

“…The bis­(dihydrogen) complex 429 adopts an octahedral geometry, where the coordinated hydrogen molecules are cis disposed with a H–H bond length of 0.906 Å. The comparison of these structures with those of their Cp-counterparts 407 and 408 reinforces the idea that Tp avoids the piano-stool structures and enforces dispositions allowing N–M–N angles close to 90°, which favor the nonclassical interactions …”