Enolphosphato−Phosphines:  A New Class of P,O Ligands

Abstract

The new bifunctional ligands Ph(2)PCH[double bond]CPh[OP(O)(OR)(2)] (1) (1a, R = Et; 1b, R = Ph) represent the first examples of P,O derivatives resulting from the association of a phosphine moiety and an enolphosphate group. The Z stereochemistry about the double bond provides a favorable situation for these ligands to act as P,O-chelates. Neutral and cationic Pd(II) complexes have been synthesized and characterized, in which 1a or 1b acts either as a P-monodentate ligand or a P,O-chelate, via coordination of the oxygen atom of the P[double bond]O group. In the latter case, it has been observed that phosphines 1a and 1b can display a hemilabile behavior, owing to successive dissociation and recoordination of the O atom. Competition experiments revealed that phosphine 1a presents a higher chelating ability than 1b, a feature ascribed to the more electrodonating properties of the ethoxy groups in 1a compared to the phenoxy groups in 1b. P,O-Chelation affords seven-membered metallocycles, which is unusual for P,O-chelates. Complexes trans-[PdCl(2)[Ph(2)PCH[double bond]C(Ph)OP(O)(OPh)(2)](2)] (2b), [PdCl[Ph(2)PCHdouble bond]C(Ph)OP(O)(OEt)(2)](mu-Cl)](2) (3a), [complex--see text] (8a'), and [complex--see text] (10a) have been structurally characterized. Interestingly, the seven-membered rings in 8a' and 10a adopt a sofa conformation with the double bond lying almost perpendicular to the plane containing the Pd, the two P, and the two O atoms.

Steric Effects of the Initiator Substituent Position on the Externally Initiated Polymerization of 2-Bromo-5-iodo-3-hexylthiophene

“…There are at least two possible explanations how steric effects could inhibit the % headgroup incorporation for In2-PPh 3 , one of which is the possible coordination of the oxygen atom of the phosphonate group to the Ni metal center, inhibiting reaction with an incoming ligand. There have been numerous reports of the PdO group coordinating to the metal center via the oxygen atom [62][63][64][65][66][67][68][69][70][71][72][73][74][75] particularly when the two are in close proximity to each other such as the case with In2-PPh 3 where the Ni 3 3 3 O distance is 3.443 A ˚. Such binding would inhibit the dppp ligand exhange reaction as was observed in the 31 P NMR and 1 H NMR, where there was significant amount of In2-PPh 3 remaining after the addition of 1.5 equiv of dppp.…”

Crystal structure of diaqua-bis(3-oxo-3,4-dihydroquinoxaline-2-carboxylato-κ2N,O)-zinc(II)-methanol-water (1:1:1), [Zn(C9H5N2O3)2(H2O)2]·CH3OH·H2O, C19H20N4O10Zn

“…In this context, aromatic carboxylate ligands, and especially N-heterocyclic carboxylates, have been intensively studied for their versatile coordination modes and potential applicability to different fields, pharmaceutical, catalyst and magnetic properties and others. These studies are extensively reported in the literature [1][2][3][4][5][6][7][8]. As a part of our continuing investigations on inorganic-organic hybrid compounds containing zinccarboxylate systems, the title complex was synthesized.…”

Poly[[diaquabis(μ2-1-oxo-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane-4-carboxylato)copper(II)] dihydrate]

“…On the other hand, from a coordination standpoint, the use of a carboxylate that contains a caged phosphate ester, such as OP(OCH 2 ) 3 CCOO À , is of interest as a ligand in generating metalorganic coordination polymers of different dimensionalities, because it may act in monodentate, bidentate and combined modes of coordination via its carboxylate group and the P O group of the caged phosphate ester, and lead to a great variety of structures. However, the literature data show that for metalphosphate ester systems, especially for complexes involving Cu, only a few complexes have been reported to date (Taylor & Waugh, 1977;Shi et al, 2001;Morise et al, 2003). Complexes of Cu and carboxylate anions with caged phosphate ester complexes are rarely reported.…”