Tetraphosphorus Ligand Research Articles

ChemInform Abstract: Recent Progress in Rhodium‐Catalyzed Hydroaminomethylation

AbstractReview: [52 refs.

Rhodium-catalyzed regioselective hydroaminomethylation of terminal olefins with pyrrole-based tetraphosphorus ligands

A protocol was developed to prepare linear amines by regioselective hydroaminomethylation of terminal olefins with pyrrole-based tetraphosphorus ligands. The reactivity of the ligand is modulated by the substituent of the biphenylphosphane moiety, with ligand L5 exhibiting the highest reactivity.

ChemInform Abstract: Rhodium‐Catalyzed Highly Regioselective Hydroaminomethylation of Styrenes with Tetraphosphorus Ligands.

AbstractIn contrast to other known methods the linear products are predominantly formed by this procedure.

Reductive Elimination at an Ortho-Metalated Iridium(III) Hydride Bearing a Tripodal Tetraphosphorus Ligand

The synthesis of the novel C3-symmetric tripodal, tetradentate ligand 1, bearing only phosphorus atoms as donor groups, is described, starting from commercially available o-tolyldiphenylphosphine, and its molecular structure has been determined by X-ray crystallographic analysis. Coordination to the cationic IrI precursor [Ir(COE)2(acetone)2]PF6 led to a highly unsymmetrical species (90% yield) with four inequivalent phosphorus atoms, as evidenced by 31P NMR spectroscopy. The corresponding 1H NMR spectrum exhibited a pseudo doublet of quartets at δ −5.9 ppm with one large trans P–H coupling (2JP–H = 115.4 Hz) and a much smaller cis coupling (2JP–H = 10.8 Hz). X-ray crystallography confirmed the formation of complex 2, [Ir(H)(κ5P,P,P,P,C-1)]PF6, which is a rare example of a structurally characterized mononuclear Ir hydride species bearing an ortho-metalated phosphine ligand. This species does not react with hydride sources, but addition of 1 equiv of CF3COOH resulted in facile overall formal protonation of the Ir–C bond. DFT calculations support a pathway involving initial reductive elimination, forming the highly distorted four-coordinate IrI species 2′, followed by protonation at iridium to give the dicationic monohydride species 3, with an activation barrier ΔG† of 28.2 kcal mol–1. Deuteration experiments support this mechanism. Reductive elimination can also be induced by reaction of 2 with carbon monoxide, yielding the monocationic carbonyl complex [IrI(CO)(1)]PF6 as the sole product.

Rhodium-Catalyzed Highly Regioselective Hydroaminomethylation of Styrenes with Tetraphosphorus Ligands

The highly linear-selective hydroaminomethylation of styrenes is very challenging. Herein, an efficient, highly chemoselective, and linear-selective hydroaminomethylation (l/b up to >99:1) of styrenes using Rh(nbd)2SbF6 with a pyrrole-based 3,3',5,5'-substituted tetraphosphorus ligand is documented. This is in sharp contrast to other available processes leading to branched amines and provides a novel atom economic approach to 3-arylpropylamines.

New Tetraphosphorus Ligands for Highly Linear Selective Hydroformylation of Allyl and Vinyl Derivatives

New tetraphosphorus ligands have been developed and applied in the rhodium-catalyzed regioselective hydroformylation of a variety of functionalized allyl and vinyl derivatives. Remarkably high linear selectivity was obtained by these tetraphosphorus ligands. The ligand that bears strong electron-withdrawing 2,4-difluorophenyl groups is the most effective one in affording linear aldehydes. The Rh/tetraphosphorus ligand catalyst is highly effective to produce linear aldehydes from functionalized allyl derivatives with heteroatoms or aromatic groups directly adjacent to the allyl group. For vinyl derivatives, the ligand is highly linear selective for acrylic derivatives, styrene, vinyl pyridine, and vinyl phthalimide. Linear to branch ratios of 26:1 and 10:1 were obtained for the hydroformylation of styrene and allyl cyanide, respectively.

Reversible P4 Activation with Nickel(I) and an η3‐Coordinated Tetraphosphorus Ligand between Two NiI Centers

P4 activation but without reduction is the most striking result of the reaction of NiI precursors (LNi) with white phosphorus. This reaction leads to the complexes 1 a and 1 b, which feature the scarce η3-coordination of the P4 ligand between two metal centers. Remarkably, 1 a undergoes facile dissociation in solution to give the paramagnetic NiI complex 2. L=β-diketiminate; 1 a: R=iPr2C6H3, 1 b: R=2,6-Et2C6H3.

Highly regioselective hydroformylation of 1,5-hexadiene to linear dialdehyde catalyzed by rhodium complexes with tetraphosphorus ligands

Rhodium-catalyzed hydroformylation of 1,5-hexadiene to corresponding dialdehydes was investigated using tetraphosphorus ligands. These ligands showed a high regioselectivity for linear aldehydes (linear to branch ratio up to 98%) in very good yield (up to 87%). It was found that the introduction of the substituents at the ortho position of the biphenyl moiety has little effect on the regioselectivity and the electron-donating substituents retard the reaction somewhat.

Highly Regioselective and Rapid Hydroformylation of Alkyl Acrylates Catalyzed by a Rhodium Complex with a Tetraphosphorus Ligand

Abstractmagnified imageAlkyl acrylates have been hydroformylated to the linear aldehydes with high regioselectivity (linear/branch>99/1) and extraordinarily high average turnover frequencies (up to 5400 h−1) by using a rhodium complex with a tetraphosphorus ligand. This protocol is in sharp contrast to the most of other processes that favor production of the branched aldehyde (typically>95% branched for most Rh‐catalyzed reaction systems). The high turnover number achieved by this new catalytic system is also remarkable considering the less reactive character of alkyl acrylates to the hydroformylation reaction conditions.

Highly Regioselective Hydroformylation of Styrene and Its Derivatives Catalyzed by Rh Complex with Tetraphosphorus Ligands

Styrene has been hydroformylated to the linear aldehyde with surprisingly high regioselectivity (l/b up to 22 for styrene) by using Rh complex with tetraphosphorus ligand. To the best of our knowledge, this is the highest linear regioselectivity reported for the hydroformylation of styrene and its derivatives. This protocol is in sharp contrast to other processes that favor producing branched aldehyde (typically >95% branched for most bidentate systems).

Highly Regioselective Isomerization−Hydroformylation of Internal Olefins to Linear Aldehyde Using Rh Complexes with Tetraphosphorus Ligands

A series of new pyrrole-based tetraphosphorus ligands were synthesized and used for Rh-catalyzed isomerization-hydroformylation of internal olefins. It was found that the substituents at the 3,3',5,5'-positions of the biphenyl greatly effected the linear selectivity, and the alkyl-substituted tetraphosphorus ligands gave the best results (for 2-octene, n: i up to 207, for 2-hexene, n: i up to 362).

A Tetraphosphorus Ligand for Highly Regioselective Isomerization−Hydroformylation of Internal Olefins

A new pyrrole-based tetraphosphorus ligand capable of forming multiple chelating modes has been prepared. Higher regioselectivity has been achieved in the rhodium-catalyzed isomerization-hydroformylations of internal olefins compared with its bisphosphorus analogue.

Hydrolytic disproportionation of coordinated white phosphorus in [CpRu(dppe)(η 1-P 4)]PF 6 [dppe = 1,2-bis(diphenylphosphino)ethane

The reaction of [CpRu(dppe)Cl] ( 1), dppe = 1,2-bis(diphenylphosphino)ethane, with one equivalent of P 4 in the presence of TlPF 6 affords the stable complex [CpRu(dppe)(η 1-P 4)]PF 6 ( 2) which contains the tetrahedral P 4 molecule η 1-bound to the metal. The tetraphosphorus ligand readily reacts with water upon mixing acetone or THF solutions of the complex with excess water. The complexes [CpRu(dppe)(PH 3)]PF 6 ( 5) and [CpRu(dppe){P(OH) 3}]PF 6 ( 6), identified among the hydrolysis products, contain the PH 3 molecule and, respectively, the unstable P(OH) 3 tautomer of the phosphorous acid bound to the CpRu(dppe) fragment. In CH 2Cl 2 the coordinated P(OH) 3 molecule in 6 easily yields the compound [CpRu(dppe){PF(OH) 2}]PF 2O 2 ( 8), via hydrolysis of the hexafluorophosphate anion and F/OH substitution in the coordinated P(OH) 3 molecule. All the compounds have been characterized by elemental analyses and NMR measurements. The crystal structures of 2 and 8 have been determined by X-ray diffraction methods.

SYNTHESIS AND STRUCTURAL PROPERTIES OF MONONUCLEAR TRANSITION METAL COMPLEXES CONTAINING NAKED TETRAPHOSPHORUS, P<SUB>4</SUB>, UNITS AS LIGAND

A summary of the known mononuclear transition metal complexes incorporating the tetraphosphorus ligand is provided. The synthesis and the main structural and bonding properties of these complexes are briefly discussed with particular emphasis given to the structural aspects of the M-ηx-P4 complexes (x=1, 2, 4) authenticated by crystallographic methods.