The catalytic activity of the palladium complex cis-[PdCl₂{($^t$BuNP(OC₆H₄OMe-𝑜))₂-$\kappa P$}₂] (2) containing cis-{$^t$BuNP(OC₆H₄OMe-𝑜)}₂ (1) in Suzuki-Miyaura and Mizoroki-Heck carbon-carbon cross coupling reactions is described. The compound 2 also displays very high activity in Mizoroki-Heck coupling reactions. The rhodium(I) complex [RhCl(COD){($^t$BuNP(OC₆H₄OMe-𝑜))₂-$\kappa P$}] (3) acts as an excellent catalyst for the hydrogenation of several terminal olefins.

The reactions of cyclodiphosphazanes, cis-[(${}^t$BuN-𝜇)₂(PNC₄H₈O)₂] (1, R = NC₄H₈O; 2, R = NC₄H₈NMe ) (2) with [{RhCl(COD)}₂] and [{RhCl(CO)₂}₂] are described. The reactions of 1 or 2 with [{RhCl(COD)}₂] in 2:1 molar ratio yielded the mononuclear complexes [(COD)RhCl{(𝜇-N$^t$BuP)₂(NC₄H₈X)₂}] (3, X = O; 4, X = NMe) in good yield. Treatment of one equivalent of [{RhCl(CO)₂}₂] with four equivalents of 1 or 2 produced the trans-[(CO)RhCl{(𝜇-N$^t$BuP)₂(NC₄H₈X)₂}₂] (5, X = O; 6, X = NMe) complexes as pale yellow solids. On changing the molar ratio of [{RhCl(CO)₂}₂] and 1 or 2 from 1:4 to 1:1 resulted in the formation of tetranuclear complexes [{(CO)Rh(𝜇-Cl)(𝜇-N$^t$BuP)(NC₄H₈X)$\}_4$] (7, X = O; 8, X = NMe) under similar reaction conditions. The tetranuclear rhodium(I) complex 8 upon stirring with wet acetonitrile or in the presence of four equivalents of water at room temperature afforded a novel hydroxo bridged zwitterionic dirhodium(I) complex [{(ClRh(CO))₂(𝜇-OH)(MeNC₄H₈N)(𝜇-N$^t$BuP)₂(NC₄H₈NHMe)}] (9). The crystal structures of 5, 6 and 9 were established by single crystal X-ray diffraction studies.

Designing efficient phosphorus-based ligands to make catalysts for homogeneous catalysis has been a great challenge for chemists. Despite a plethora of phosphorus ligands ranging from simple tertiary phosphines to polyphosphines are known, the enthusiasm to generate new ones is mainly due to the demand from industry for economical and robust catalytic system operational under normal atmospheric conditions. In this context, we have developed new synthetic methodologies for making unusual inorganic ring systems containing trivalent phosphorus centres, novel phosphorus-based multidentate and hybrid ligands and explored their rich transition metal chemistry and catalytic applications. We have also fine tuned a few existing ligand systems with donor functionalities to employ them in homogeneous catalysis. The details are summarized in this account.

The bisphosphomide-based pincer complex [PdBr{2,6-{Ph₂PC(O)}₂(C₆H₃)}] (2) has shown very high catalytic activity in Suzuki-Miyaura cross coupling reaction under microwave irradiation for a variety of aryl bromides and aryl boronic acids. The complex showed the same efficiency for gram scale reactions.

The reaction of 2,3-bis(bromomethyl)quinoxaline with imidazole afforded the quinoxaline bridged diimidazolium salt (1) in good yield. Diimidazolium salt (1) in conjunction with Pd(OAc)₂ was employed as a catalyst for C–C cross-coupling reactions. The diimidazolium salt was found to be efficient in catalyzing Suzuki-Miyaura cross-coupling reaction in ethanol under ambient conditions. Moderate to good selectivity of the trans product was observed in the Heck cross-coupling reaction. The molecular structure of 1 was confirmed by single crystal X-ray diffraction study.

The hydrolysis of cis-{ClP(𝜇-N$^t$Bu)2P(NH$^t$Bu)} (1) produced a mixed P^III/P^V derivative of cyclodiphosphazane, cis-{($^t$BuNH)P(𝜇-N$^t$Bu)₂P(O)H} (2). The treatment of 2 with elemental selenium resulted in the formation of the monoselenide, trans-{($^t$BuNH)P(Se)(𝜇-N$^t$Bu)₂P(O)H} (3) in good yield. The reactions of two equivalent of 2 with [Pd(𝜇-Cl)(𝜂³-C₃H₅)]₂ or [Ru(𝜂⁶-𝑝-cymene)(𝜇-Cl)Cl]₂ in dichloromethane afforded corresponding mononuclear complexes, [(𝜂³-C₃H₅)PdCl{($^t$BuNH)P(𝜇-N$^t$Bu)₂P(O)H}] (4) and [((𝜂⁶-𝑝-cymene)RuCl₂){($^t$BuNH)P(𝜇-N$^t$Bu)₂P(O)H}] (5). The treatment of 2 with M(COD)Cl₂ (M = Pd and Pt) in dichloromethane at room temperature gave [MCl₂{($^t$BuNH)P(𝜇-N$^t$Bu)₂P(O)H}₂] (6 M = Pd; 7 M = Pt) in good yield. Owing to the cis/trans isomerisation of the cyclodiphosphazane rings, the complexes 6 and 7 exist as a mixture of two isomers. Various NMR spectroscopic techniques were employed for structural elucidation. The molecular structures of 5 and 7 were established by single crystal X-ray crystallographic studies.

Photophysical studies of luminescent gold complex of triphenylphosphole has been described. Addition of biologically relevant thio compounds was found to quench its fluorescence in methanol solution. Based on this, a simple and selective luminescence sensing method for cysteine detection has been developed.