Design and synthesis of versatile ligand precursors based on phosphonium ylides for palladalactam formation and catalytic investigation

A new series of ligand precursors designed for the synthesis of palladalactams has been developed. These precursors are easily accessible through a one-step reaction involving 2-chloro-N-phenylacetamide and a wide choice of various monophosphines, offering tunable electronic and steric properties within the ligand framework. The stability of both ligand precursors and resulting palladalactams in ambient air enhances their practical applicability. A newly synthesized palladalactam, featuring an electron-donating triethylphosphine moiety on the anionic phosphonium ylide ligand scaffold exhibited promising catalytic activities in the Mizoroki-Heck coupling reaction between aryl chlorides and alkenes. Theoretical calculations further affirmed that the ligand system in the complex is the most electron-donating, forming the strongest Pd-C bond compared to other complexes with alternative phosphine moieties.

Crystal structure of bis-(3,3-dimethyl-2-oxobut-yl)di-phenyl-phospho-nium bromide chloro-form monosolvate

In the title salt solvate, C24H32O2P(+)·Br(-)·CHCl3, the P atom has a distorted tetra-hedral geometry, and the planes of the phenyl rings form a dihedral angle of 71.86 (14)° with one another. The bromide anion is disordered and was modelled over three positions (occupancy ratio 0.50:0.35:0.15). The crystal also contains one disordered chloro-form solvent mol-ecule that was modeled over three positions (occupancy ratio 0.50:0.35:0.15). Weak inter-molecular inter-actions (C-H⋯Br and C-H⋯O) exist between the complex cation and the bromide anion fragments. The resulting supramolecular structure is an oval-shaped arrangement of phosphonium salt molecules that surround the disordered bromide anion.

Synthesis and Structure of Pd(II) Complexes Containing the C,C-Chelating Bis-Ylide Ligand [Ph(3)P=C(H)](2)CO. X-ray Crystal Structure of {Pd(&mgr;-Cl){[C(H)PPh(3)](2)CO}}(2)(ClO(4))(2).CH(2)Cl(2)

The reaction of Pd(OAc)(2) with the bis(phosphonium) salt [Ph(3)PCH(2)COCH(2)PPh(3)]Cl(2) (1:1 molar ratio) results in the formation of the cis-dichlorobis(ylide) derivative Cl(2)Pd{[C(H)PPh(3)](2)CO}, 1, in which the bis(ylide) ligand [C(H)PPh(3)](2)CO acts as a chelating group through the two ylide carbon atoms. Complex 1 reacts with TlClO(4) (1:1 molar ratio) to give [Pd(&mgr;-Cl){[C(H)PPh(3)](2)CO}](2)(ClO(4))(2), 2, which reacts with two further equivalents of TlClO(4) in NCMe to give [Pd{[C(H)PPh(3)](2)CO}(NCMe)(2)](ClO(4))(2) 3. The reactivity of 2 and 3 has been explored. Compound 2 reacts with pyridine, 3,5-lutidine, or Ph(3)P=C(H)CN (1:2 molar ratio), resulting in the rupture of the chlorine bridging system and formation of [PdCl{[C(H)PPh(3)](2)CO}(L)](ClO(4)) (L = py (4), 3,5-lu (5), NC-C(H)=PPh(3) (6)), and with Tlacac (1:2 molar ratio) with formation of the acetylacetonate [Pd(acac){[C(H)PPh(3)](2)CO}](ClO(4)), 7. On the other hand, complex 3 reacts with the ylide Ph(3)P=C(H)CN (1:2 molar ratio) giving [Pd{[C(H)PPh(3)](2)CO}[NC-C(H)=PPh(3)](2)](ClO(4))(2), 8, which contains two N-coordinated ylides, and with NBu(4)OH (1:1) to give [Pd(&mgr;-OH){[C(H)PPh(3)](2)CO}](2)(ClO(4))(2), 9. The reaction of Pd(OAc)(2) with the ylide phosphonium salt [Ph(3)P=C(H)COCH(2)PPh(3)](ClO(4)) (1:1) gives the acetate dimer [Pd(&mgr;-OOCCH(3)){[C(H)PPh(3)](2)CO}](2)(ClO(4))(2), 10. The structures of complexes 1-10 were deduced from their spectroscopic data and from the resolution of the molecular structure of complex 2.CH(2)Cl(2).

Platinum-Assisted Addition of Carbonyl-Stabilized Phosphorus Ylides to Pentafluorobenzonitrile and Acetonitrile To Give Platinum(II) Complexes Containing Iminophosphorane and/or N-Bonded beta-Imino Phosphorus Ylide Ligands. Crystal and Molecular Structures of trans-[PtCl(2){E-NH=C(C(6)F(5))C(=PPh(3))C(O)Me}(2)] and trans-[PtCl(2){E-N(=PPh(3))C(C(6)F(5))=CHCO(2)Et}{E-NH=C(C(6)F(5))C(=PPh(3))CO(2)Et}]

PtCl(2) reacts with C(6)F(5)CN to give trans-[PtCl(2)(NCC(6)F(5))(2)] (1) which, in turn, reacts with carbonyl-stabilized phosphorus ylides Ph(3)P=CHR [R = C(O)Me, CO(2)Et] to give trans-[PtCl(2){NH=C(C(6)F(5))C(=PPh(3))CO(2)Et}{NCC(6)F(5)}] (2a), trans-[PtCl(2){NH=C(C(6)F(5))C(=PPh(3))CO(2)Et}(2)] (3a), trans-[PtCl(2){E-NH=C(C(6)F(5))C(=PPh(3))C(O)Me}(2)] (3b) or trans-[PtCl(2){E-N(=PPh(3))C(C(6)F(5))=CHCO(2)Et}{E-NH=C(C(6)F(5))C(=PPh(3))CO(2)Et}] (4), depending on the reaction conditions. Similarly, Ph(3)P=CHCO(2)Me reacts with trans-[PtCl(2)(NCMe)(2)] to give trans-[PtCl(2){NH=CMeC(=PPh(3))CO(2)Me}(NCMe)] (2b). Complex 3b.CH(2)Cl(2) crystallizes in the triclinic system, space group P&onemacr;, with a = 7.596(2) Å, b = 12.694(3) Å, c = 16.962(3) Å, alpha = 104.28(3) degrees, beta = 102.73(3) degrees, gamma = 104.43(3) degrees, V = 1464.2(6) Å(3), and Z = 1. The structure was refined to values of R1 = 0.0411 and wR2 = 0.1172 [I >2sigma(I)] and shows two chloro and two N-bonded beta-imino phosphorus ylide ligands in a trans geometry. Complex 4 crystallizes in the monoclinic system, space group P2(1)/c, with a = 16.400(8) Å, b = 14.354(7) Å, c = 23.221(12) Å, alpha = 90(3) degrees, beta = 92.42(2) degrees, gamma = 90 degrees, V = 5462(5) Å(3), and Z = 4. The structure was refined to values of R1 = 0.0246 and wR2 = 0.0557 [I >2sigma(I)]. This complex has also a trans-geometry and shows that while the attack of the ylide on one of the nitrile ligands produces a beta-imino-phosphorus ylide ligand the addition on the second nitrile leads to an iminophosphorane ligand.