Sterically Demanding Phosphines with 2,6-Dibenzhydryl-4-methylphenyl Core: Synthesis of Ru^II, Pd^II, and Pt^II Complexes, and Structural and Catalytic Studies

Abstract

The synthesis of sterically demanding aminophosphine and phosphinite ligands Ar*NHPPh (1) and Ar*OPPh (2), based on 2,6-dibenzhydryl-4-methylphenyl core having bulky benzhydryl groups, and their Ru, Pd and Pt complexes is described. The reactions of 1 and 2 with [Ru(η- p-cymene)Cl] in 2:1 molar ratios produced mononuclear complexes [RuCl{(η- p-cymene)PPh-EAr*}-κ-P] (E = NH (3) and O (4)). Interestingly, complexes 3 and 4, upon refluxing in chlorobenzene, displace the p-cymene ring by one of the phenyl rings of side arms, forming rare η-arene coordinated tethered complexes [RuCl{(PPh-EAr*)-κ-P-η-arene}] (E = NH (5) and O (6)). Treatment of 1 and 2 with [M(COD)Cl] [M = Pd, Pt] in 2:1 ratios afforded mononuclear complexes [MCl{(PPhEAr*)-κ-P}] (E = NH, M= Pd (7), Pt (8); E = O, M= Pd (9), Pt (10)). Similarly, 1:1 reactions of 1 and 2 with [Pd(COD)Cl] produced chloro-bridged dinuclear complexes [PdCl{(PPhEAr*)-κ-P}] (E = NH (11) and O (12)), whereas [Pt(COD)Cl] yielded only the mononuclear complexes 8 and 10. The reactions of 1 and 2 with [Pd(η-CH)Cl] in 2:1 molar ratios produced the mononuclear complexes [PdCl{(η-CH)(PPhEAr*)-κ-P}] (E = NH (13) and O (14)). Many of these complexes have been structurally characterized, which show C-H···π interactions between the methine hydrogen of the benzhydryl and with one of the carbon atoms of the phenyl ring attached to the phosphorus center. The complex [RuCl{(η- p-cymene)PPh-NHAr*}-κ-P] (3) shows very short C-H···π interactions of 2.36 Å; in addition, C-H···M interactions were observed between the methine hydrogen of one of the benzhydryl groups and palladium centers in 11 and 13. The tethered ruthenium complex 5 is found to be an excellent catalyst for the catalytic oxidation of various styrene derivatives.

Rare Au···H Interactions in Gold(I) Complexes of Bulky Phosphines Derived from 2,6-Dibenzhydryl-4-methylphenyl Core

“…All the solvents used in this study were dried by conventional methods and distilled before use. [Ar*NH 2 ], 52 [Ar*NHPPh 2 ] (3), 23 [Ar*OPPh 2 ] (4), 23 HPPh 2 , 53 and [AuCl-(SMe 2 )] 54 were prepared according to the published procedures. AgSbF 6 was purchased from Aldrich Chemicals and used without purification, and other reagents were obtained from commercial sources and used after purification.…”

“…Gold complexes of phosphines have gained considerable attention in recent times due to their importance in catalysis, − photophysical, and biological applications. , The effective intra- and intermolecular aurophilic interactions have significantly diversified the coordination chemistry of gold complexes resulting in supramolecular architectures and molecular aggregations, in both the solid and solution states. − The best way to enhance these interactions is by using the short-bite bidentate ligands, which can bring the metal ions in close proximity. , Gold­(I) complexes generally prefer linear geometry featuring intra- ( B ) ,,− or intermolecular ( C ) ,,− aurophilic interactions. Sterically demanding phosphines with aromatic groups either on or close to the phosphorus atoms are particularly interesting due to their ability to facilitate metal arene interactions and also rare M···H interactions. − The possible structural motifs for digold complexes of bisphosphine are shown in Chart . Short bite ligands afford complexes of type B – C , ,, whereas large-bite and sterically bulky bisphosphines might afford complexes of type A or D .…”

Facile Arene Ligand Exchange in p-Cymene Ruthenium(II) Complexes of Tertiary P-Chiral Ferrocenyl Phosphines

“…Tethered complexes are an interesting subset of metal–arene complexes which emerge when the π-coordinating neutral arene ligand is connected with one of the coordinating donor groups. Here, phosphines with pendant aromatic groups in close proximity to the phosphorus atom are predominantly used as polydentate ligands for the formation of tethered ruthenium complexes. − Utilizing the chelate effect to stabilize the arene–metal interaction is one major benefit of tethered complexes compared to nontethered complexes. , In the case of chiral ligands, another advantage is a restrained stereochemical situation which raises the racemization barrier of the chiral tethered complex. ,− The arene coordination to form tethered complexes can be triggered thermally, but usually requires high temperatures . In contrast, tethering triggered by light is a milder alternative in cases where thermal racemization needs to be avoided, for example, with P -stereogenic phosphines …”

Half-Sandwich Arene-Osmium(II) Complexes with Phosphinite Ligands

“…Selected bond distances (Å) and angles (deg): Os(1)-C* = 1.1706(2); Os(1)-Cl(1) = 2.408(2); Os(1)-Cl(2) = 2.406(2); Os(1)-P(1) = 2.318(2); P(1)-O(1) = 1.611(4); P(1)-C(11) = 1.803(6); P(1)-C(17) = 1.823(6); Os(1)-C(23) = 1.448 (7); C*-Os(1)-P(1) = 127.47(4); C*-Os(1)-Cl(1) = 125.55(5); C*-Os(1)-Cl(2) = 127.96(4); Cl(1)-Os(1)-Cl(2) = 86.83 (7); (4); C* denotes the centroid of the p-cymene ring (C(2), C(3), C(4), C(5), C(6) and C (7)).…”

“…These compounds are of interest as they represent rare examples of tethered arene-ruthenium(II) complexes incorporating pendant phosphinite donors [2][3][4], a field largely dominated by the use of arene ligands featuring classical phosphines as the pendant donor group [1,5]. Moreover, we also demonstrated their utility as catalysts for the cross dehydrogenative coupling of hydrosilanes with alcohols [1], a process of relevance since it allows a simple access to useful alkoxysilane reagents [6,7], and with potential application in the field of hydrogen storage and production [8].…”