Cage Phosphinites: Ligands for Efficient Nickel-Catalyzed Hydrocyanation of 3-Pentenenitrile

Welcoming Neighbour or Inhospitable Host? Selective Second Metal Binding in 5- and 6-Phospha-Substituted Bpy Ligands

The controlled formation of mixed-metal bimetallics was realised through use of a fac-[Re(CO)3(N,N'-bpy-P)Cl] complex bearing an exogenous 2,4,6-trioxa-1,3,5,7-tetramethyl-8-phosphaadamantane donor at the 5-position of the bpy. The introduction of gold, silver, and rhodium with appropriate secondary ligands was readily achieved from established starting materials. Restricted rotation about the C(bpy)-P bond was observed in several of the bimetallic complexes and correlated with the relative steric bulk of the second metal moiety. Related chemistry with the 6-substituted derivative proved more limited in scope with only the bimetallic Re/Au complex being isolated.

Dioxaphosphabicyclooctanes: small caged phosphines from tris(hydroxymethyl)phosphine

Dioxaphosphabicyclo[2.2.2]octanes (L1-L4) have been prepared in a one-pot reaction from tris(hydroxymethyl)phosphine and various α,β-unsaturated ketones. The non-volatile phosphines oxidise very slowly in air. They possess highly upfield 31P chemical shifts (-59 to -70 ppm), small cone angles (121-140°) and a similar electronic parameter to PPh3. Reaction of L1 with [Rh(acac)(CO)2] gave the complex [Rh(acac)(CO)(L1)] with a ν(CO) of 1981.5 cm-1, whereas reaction L1 with [Rh(CO)2Cl]2 gave [Rh(CO)(L1)2Cl] with a ν(CO) of 1979.9 cm-1, remarkably similar to the CO stretching frequencies reported for analogous PPh3 complexes. The cage phosphines were explored as ligands in rhodium catalysed hydroformylation of 1-octene. All of the ligands gave a linear selectivity to n-nonanal of 68%, regardless of the substituents. However the ligand substituents had a significant effect on the catalyst activity, with increased steric bulk around the coordination environment giving a three-fold increase in aldehyde yield. The phosphines undergo ligand subsitution with [Pd(MeCN)2Cl2] forming square planar trans-[Pd(L)2Cl2] complexes. Subsequent reduction with hydrazine furnishes homoleptic tetravalent [Pd(L1)4] which was applied as a catalyst in Suzuki-Miyaura couplings, furnishing the C-C coupled products in moderate yields.

A comprehensive review of caged phosphines: synthesis, catalytic applications, and future perspectives

Caged phosphines are versatile ligands due to their rigid backbones, exhibiting a range of catalytic activities, as depicted through the given pictorial representation.

Mechanistic Study of Unprecedented Highly Regioselective Hydrocyanation of Terminal Alkynes: Insight into the Origins of the Regioselectivity and Ligand Effects

Density functional theory (DFT) calculations were performed to gain insight into the mechanism of the nickel-catalyzed hydrocyanation of terminal alkynes with Zn(CN)₂ and water to exclusively generate the branched nitrile with excellent Markovnikov selectivity. After precatalyst activation to give the LNi(0) active species, the transformation proceeds via the following steps: (1) oxidative addition of H₂ O to the LNi(0) provides the intermediate LNi(II)H(OH); (2) ligand exchange of LNi(II)H(OH) with Zn(CN)₂ gives the intermediate LNi(II)H(CN); (3) alkyne insertion to the LNi(II)H(CN) forms the alkenyl nickel complex, followed by the reductive elimination step reaching the final product. This mechanism is kinetically and thermodynamically more favorable than that of the experimental proposed ones. On the basis of the experimental observations, more water molecules cannot further improve the reaction as it has also been rationalized. Furthermore, the origin of the high regioselectivity of the product, the variable effectiveness of the metal mediator as function of ligands, as well as the high yield of the alkyl-substituted alkynes substrates, is analyzed in detail. © 2019 Wiley Periodicals, Inc.

Oxalamide-based bisdiamidophosphites: synthesis, coordination, and application in asymmetric metallocatalysis

A new group of P*-chiral bisdiamidophosphites has been developed for Pd- and Rh-catalyzed asymmetric reactions with good to excellent enantioselectivities.

Amidine functionalized phosphines: tuneable ligands for transition metals

A diastereomeric, cationic phosphine ligand [α,β-CgPAmMe]⁺ composed of a chiral amidinium substituent and a racemic phosphacycle has been prepared and compared to its neutral parent α,β-CgPAm.

Challenging nickel-catalysed amine arylations enabled by tailored ancillary ligand design

Palladium-catalysed C(sp(2))-N cross-coupling (that is, Buchwald-Hartwig amination) is employed widely in synthetic chemistry, including in the pharmaceutical industry, for the synthesis of (hetero)aniline derivatives. However, the cost and relative scarcity of palladium provides motivation for the development of alternative, more Earth-abundant catalysts for such transformations. Here we disclose an operationally simple and air-stable ligand/nickel(II) pre-catalyst that accommodates the broadest combination of C(sp(2))-N coupling partners reported to date for any single nickel catalyst, without the need for a precious-metal co-catalyst. Key to the unprecedented performance of this pre-catalyst is the application of the new, sterically demanding yet electron-poor bisphosphine PAd-DalPhos. Featured are the first reports of nickel-catalysed room temperature reactions involving challenging primary alkylamine and ammonia reaction partners employing an unprecedented scope of electrophiles, including transformations involving sought-after (hetero)aryl mesylates for which no capable catalyst system is known.

Organomonophosphines in PtP2Cl2 derivatives: structural aspects

In this review, 260 monomeric Pt(II) complexes are summarized and analyzed in which the inner coordination sphere is built up by a pair of organomonophosphines and two chlorine atoms (PtP2Cl2). These complexes are crystallized in four crystal systems: tetragonal (x17)<orthorhombic (x31)<triclinic (x90)<monoclinic (x122). The square-planar environments have cis- and trans-configurations. The former by far prevails. The mean Pt-L bond distances (cis- vs. trans-configurations) are 2.347 Å (Cl, trans to P) and 2.230 Å (P, trans to Cl) vs. 2.307 Å (Cl, trans to Cl) and 2.320 Å (P, trans to P). There are two types of isomerisms: cis-, trans- and distortion. In general, the derivatives with a cis-configuration are somewhat more distorted than that with a trans-configuration.

Effective donor abilities of E-t-Bu and EPh (E = O, S, Se, Te) to a high valent transition metal

Amido rotation in the chromium(vi), d(0)-system NCr(NPr(i)2)2X is under investigation as a method for the parameterization of ligands for their donor properties toward high valent metals. In this study, two new series were prepared and studied based on chalcogenide ligands, X = EBu(t) and EPh and where E = O, S, Se, Te; the OPh and SPh compounds were previously reported. The ligand donor parameters for these ligands correlate with the Cr-E-C angles in these chalcogenide series. In addition, it was found that NBO calculated overlaps and DFT calculated bond dissociation enthalpies correlate within X = halide-, EBu(t)- and EPh-series. All of the new complexes were characterized by X-ray diffraction.

Evaluation of donor and steric properties of anionic ligands on high valent transition metals

Synthetic protocols and characterization data for a variety of chromium(VI) nitrido compounds of the general formula NCr(NPr(i)(2))(2)X are reported, where X = NPr(i)(2) (1), I (2), Cl (3), Br (4), OTf (5), 1-adamantoxide (6), OSiPh(3) (7), O(2)CPh (8), OBu(t)(F6) (9), OPh (10), O-p-(OMe)C(6)H(4) (11), O-p-(SMe)C(6)H(4) (12), O-p-(Bu(t))C(6)H(4) (13), O-p-(F)C(6)H(4) (14), O-p-(Cl)C(6)H(4) (15), O-p-(CF(3))C(6)H(4) (16), OC(6)F(5) (17), κ(O)-N-oxy-phthalimide (18), SPh (19), OCH(2)Ph (20), NO(3) (21), pyrrolyl (22), 3-C(6)F(5)-pyrrolyl (23), 3-[3,5-(CF(3))(2)C(6)H(3)]pyrrolyl (24), indolyl (25), carbazolyl (26), N(Me)Ph (27), κ(N)-NCO (28), κ(N)-NCS (29), CN (30), NMe(2) (31), F (33). Several different techniques were employed in the syntheses, including nitrogen-atom transfer for the formation of 1. A cationic chromium complex [NCr(NPr(i)(2))(2)(DMAP)]BF(4) (32) was used as an intermediate for the production of 33, which was produced by tin-catalyzed degredation of the salt. Using spin saturation transfer or line shape analysis, the free energy barriers for diisopropylamido rotation were studied. It is proposed that the estimated enthalpic barriers, Ligand Donor Parameters (LDPs), for amido rotation can be used to parametrize the donor abilities of this diverse set of anionic ligands toward transition metal centers in low d-electron counts. The new LDPs do not correlate well to the pK(a) value of X. Conversely, the LDP values of phenoxide ligands do correlate with Hammett parameters for the para-substituents. Literature data for (13)C NMR chemical shifts for a tungsten-based system with various X ligands plotted versus LDP provided a linear fit. In addition, the angular overlap model derived e(σ) + e(π) values for chromium(III) ammine complexes correlate with LDP values. Also discussed is the correlation with XTiCp*(2) spectroscopic data. X-ray diffraction has been used used to characterize 31 of the compounds. From the X-ray diffraction data, steric parameters for the ligands using the Percent Buried Volume and Solid Angle techniques were found.