Rapid phosphorus(iii) ligand evaluation utilising potassium selenocyanate

Abstract

Oxidative addition of SeCN(-) to tertiary phosphine ligands has been investigated in methanol at 298 K by use of UV-Vis stopped-flow and conventional spectrophotometry. In most cases k(obs) vs. [SeCN(-)] plots were linear with zero intercepts corresponding to a rate expression of k(obs) = k(1)[SeCN(-)]. Reactions rates are dependent on the electron density of the phosphorus centre with k(1) varying by five orders of magnitude from 1.34 +/- 0.02 x 10(-3) to 51 +/- 3 mol(-1) dm(3) s(-1) for P(2-OMe-C(6)H(4))(3) to PCy(3) respectively. Activation parameters range from 27 +/- 1 to 49.0 +/- 1.3 kJ mol(-1) for DeltaH(double dagger) and -112 +/- 9 to -140 +/- 3 J K(-1) mol(-1) for DeltaS(double dagger) supporting a S(N)2 mechanism in which the initial nucleophilic attack of P on Se is rate determining. Reaction rates are promoted by more polar solvents supporting the mechanistic assignment. Reasonable linear correlations were observed between log k(1)vs. pK(a), (1)J(P-Se) and chi(d) values of the phosphines. The reaction rates are remarkably sensitive to the steric bulk of the substituents, and substitution of phenyl rings in the 2 position resulted in a decrease in the reaction rate. The crystal structures of SePPh(2)Cy and SePPhCy(2) have been determined displaying Se-P bond distances of 2.111(2) and 2.1260(8) A respectively.

Crystal structure of N,N-bis(diphenylphosphanyl)cyclohexylamine, C30H31NP2

“…The modular structure of the ligands enables "tuning" of the catalyst activity and selectivity through systematic variation of the donor atoms, their substituents, and the ligand backbone framework. There are numerous examples of crystal structures of such PNP-pincer ligands [1][2][3][4][5][6] and metal complexes [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]. Diphosphinoamine (PNP) and other P donor ligands [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] with various substituents on both the P and N atoms have been applied to several catalytic reactions such as methoxycarbonylation [17], metathesis [18], hydroformylation [19] and C-H activation [24].…”

Crystal structure of dichlorido bis(2-methylbenzothiazole-κ 1N)palladium( II) chloride, C16H14Cl2N2PdS2

“…the oxygen atom with sulphur atom to study the effect on coordination behaviour of these ligands [7][8][9][10]. However the cyclization process to form benzothiazoles often prevents the formation of these types of ligands [11][12][13].…”

Amidoamine-based dendrimers with end-grafted Pd–Fe units: Synthesis, characterization and their use in the Heck reaction

“…After appropriate work-up, 5-FeeSe and 9-FeeSe were isolated as orange solids in almost quantitative yield (Section 4). The phosphoruseselenium coupling constants of 5-FeeSe and 9-FeeSe were determined to 1 J ( 31 Pe 77 Se) ¼ 720 Hz (5-FeeSe) and 723 Hz (9-FeeSe), being slightly decreased, when compared with FcPh 2 P ¼ Se 1 J ( 31 Pe 77 Se) ¼ 731 Hz) and Ph 3 P ¼ Se ( 1 J ( 31 P e 77 Se) ¼ 729 Hz) [25]. Obviously, the immobilization on the scaffold has no negative impact on the s-donor properties of the phosphines.…”