First Dibenzophospholyl(diphenylphosphino)methane−Borane Hybrid P−(η2-BH3) Ligand: Synthesis and Rhodium(I) Complex

Three-Center M-H-B Bonds Are Strong Field Interactions. Synthesis and Characterization of M(CH2NMe2BH3)3 Complexes of Titanium, Chromium, and Cobalt

We describe new compounds of stoichiometry M(CH2NMe2BH3)3 (M = Ti, Cr, and Co), each of which contains three chelating boranatodimethylaminomethyl (BDAM) ligands. In all three compounds, the BDAM anion, which is isoelectronic and isostructural with the neopentyl group, is bound to the metal center at one end by a metal-carbon σ bond and at the other by one three-center M-H-B interaction. The crystal structures show that the d1 titanium(III) compound is trigonal prismatic (or eight-coordinate, if two longer-ranged M···H interactions with the BH3 groups are included), whereas the d3 chromium(III) compound and the d6 cobalt(III) compounds are both fac-octahedral. The Cr and Co compounds exhibit two rapid dynamic processes in solution: exchange between the Δ and Λ enantiomers and exchange of the terminal and bridging hydrogen atoms on boron. For the Co complex, the barrier for Δ/Λ exchange (ΔG⧧298 = 10.1 kcal mol-1) is significantly smaller than those seen in other octahedral cobalt(III) compounds; DFT calculations suggest that Bailar twist and dissociative pathways for Δ/Λ exchange are both possible mechanisms. The UV-vis absorption spectra of the cobalt(III) and chromium(III) species show that the ligand field splittings Δo caused by the M-H-B interactions are unexpectedly large, thus placing them high on the spectrochemical series (near ammonia and alkyl groups); their nephelauxetic effect is also large. The DFT calculations suggest that these properties of M-H-B interactions are in part a consequence of their three-center nature, which delocalizes electron density away from the metal center and reduces electron-electron repulsions.

E-Selective Synthesis and Coordination Chemistry of Pyridine-Phosphaalkenes: Five Ligands Produce Four Distinct Types of Ru(II) Complexes

Pyridine-phosphaalkene (PN) ligands 2a-e were prepared in an E-selective fashion using phospha-Wittig methodology. Treatment of these five ligands, varying only in their 6-substituent with RuCl₂(PPh₃)₃, produced four distinct types of coordination complexes: pyridine-phosphaalkene-derived 3b,d, cyclized 4e, and six-coordinate 5a and 6c. Prolonged heating of 3b,d in THF resulted in C-H activation of the Mes* group and cyclization to give 4b,d featuring a bidentate pyridine-phospholane ligand bound to the metal center. Complex 5a, also possessing a newly formed phospholane ring, contained a different spatial arrangement of donors to Ru(II) with an agostic Ru-H-C interaction serving as the sixth donor to the transition metal center. Ligands 2b,d,e and Ru(II) complexes 3b, 4b,e and 5a were all characterized by X-ray crystallography. Six-coordinate 6c featured a structure similar to 4b,d,e, but with the CF₃ substituent acting as a weakly bound sixth ligand to the Ru(II) center, as observed by ³¹P{¹H} and¹⁹F NMR spectroscopy. The calculated structure of 6c established that the closest Ru- - -F contact was at 2.978 Å.

Recent studies of the synthesis, functionalization, optoelectronic properties and applications of dibenzophospholes

The dibenzophospholes, synthesized in the 1950s, have recently gained a greater importance, due to their use in organic electronics and the possibility of designing new π-conjugated, optoelectronic materials that incorporate these heterocycles.

Octahedral manganese(i) and ruthenium(ii) complexes containing 2-(methylamido)pyridine–borane as a tripod κ3N,H,H-ligand

The borane adduct of the 2-(methylamido)pyridine anion has been incorporated into octahedral metal (Mn, Ru) complexes and their bonding has been studied by theoretical methods (DFT, QTAIM).

Phosphole-based ligands in catalysis

This review provides an overview of phosphole-based ligand families (monophospholes, multidentate hybrid phosphole ligands, diphosphole and 2,2′-biphosphole-based ligands) and their potential in metal- and organo-catalyzed reactions (asymmetric reactions included).

Effect of the phosphine steric and electronic profile on the Rh-promoted dehydrocoupling of phosphine-boranes

The electronic and steric effects in the stoichiometric dehydrocoupling of secondary and primary phosphine–boranes H₃B·PR₂H [R = 3,5-(CF₃)₂C₆H₃; p-(CF₃)C₆H₄; p-(OMe)C₆H₄; adamantyl, Ad] and H₃B·PCyH₂ to form the metal-bound linear diboraphosphines H₃B·PR₂BH₂·PR₂H and H₃B·PRHBH₂·PRH₂, respectively, are reported. Reaction of [Rh(L)(η⁶-FC₆H₅)][BAr^F₄] [L = Ph₂P(CH₂)₃PPh₂, Ar^F = 3,5-(CF₃)₂C₆H₃] with 2 equiv of H₃B·PR₂H affords [Rh(L)(H)(σ,η-PR₂BH₃)(η¹-H₃B·PR₂H)][BAr^F₄]. These complexes undergo dehydrocoupling to give the diboraphosphine complexes [Rh(L)(H)(σ,η²-PR₂·BH₂PR₂·BH₃)][BAr^F₄]. With electron-withdrawing groups on the phosphine–borane there is the parallel formation of the products of B–P cleavage, [Rh(L)(PR₂H)₂][BAr^F₄], while with electron-donating groups no parallel product is formed. For the bulky, electron rich, H₃B·P(Ad)₂H no dehydrocoupling is observed, but an intermediate Rh(I) σ phosphine–borane complex is formed, [Rh(L){η²-H₃B·P(Ad)₂H}][BAr^F₄], that undergoes B–P bond cleavage to give [Rh(L){η¹-H₃B·P(Ad)₂H}{P(Ad)₂H}][BAr^F₄]. The relative rates of dehydrocoupling of H₃B·PR₂H (R = aryl) show that increasingly electron-withdrawing substituents result in faster dehydrocoupling, but also suffer from the formation of the parallel product resulting from P–B bond cleavage. H₃B·PCyH₂ undergoes a similar dehydrocoupling process, and gives a mixture of stereoisomers of the resulting metal-bound diboraphosphine that arise from activation of the prochiral P–H bonds, with one stereoisomer favored. This diastereomeric mixture may also be biased by use of a chiral phosphine ligand. The selectivity and efficiencies of resulting catalytic dehydrocoupling processes are also briefly discussed.

The effect of changing the steric and electronic profile of the phosphine of primary and secondary phosphine−boranes H₃B·PR₂H (R = H, aryl, adamantyl) on the Rh-catalyzed dehydrocoupling to form metal-bound linear diboraphosphines is reported.

Novel phospholyl(diphenylphosphino)methane-ruthenium complexes: unexpected non-assisted cis to trans isomerization of [RuCl2(κ(2)-P-P')2]

Using the unsymmetrical P-P' phospholyl(phosphino)methane ligand, complex cis-[RuCl(2)(κ(2)-P-P')(2)] is easily prepared from [RuCl(2)(DMSO)(4)]. The two phosphole-phosphorus atoms lie in the trans position to the two cis-chloro ligands. This complex slowly isomerizes spontaneously at 20 °C to the trans-[RuCl(2)(κ(2)-P-P')(2)] diastereoisomer where the two phosphole moieties are mutually trans, as well as the two chloro ligands and the two Ph(2)P moieties. DFT calculations show that this non-classical cis-trans isomerisation process requires a 3 kcal mol(-1) energy and involves the decoordination of a phosphole arm.