Versatility of Iminophosphoranes and Noninnocent Behavior of the 1,5-Cyclooctadiene Ligand in Palladium(II) Complexes. Synthesis of σ-Allyl Derivatives

Abstract

The treatment of PdCl 2 (NCPh) 2 with Ph 3 PdNPh (1) gives the expected complex trans-PdCl 2 [N(Ph)-PPh 3 ] 2 (3). However, the reaction of PdCl 2 (COD) (COD ) 1,5-cyclooctadiene) with 1 or Ph 3 PdN-1-Np (2) (Np ) naphthyl) occurs through nucleophilic attack of 1 or 2 on one olefinic bond of the COD ligand followed by proton abstraction on the adjacent methylene group, giving the η 1 -allyl complexes [Ph 3 P(R)NH‚‚‚Cl 2 Pd(C 8 H 11 )] (R ) Ph, 4; Np, 5). The X-ray structure of 4 has been determined and shows two interesting facts: (i) the η 1 -η 2 -bonded cyclooctadienyl ligand, containing a η 1 -allyl fragment, and (ii) the presence of a strong H bond between one of the Cl ligands and the proton of the NH group. This H bond persists in solution, as shown by NMR and molar conductance measurements. The abstraction of a chloride on 4 by reaction with AgClO 4 cleaves the H bond and gives a mixture of the salt [Ph 3 PN-(H)Ph](ClO 4 ) ( 6) and the neutral η 1 -η 2 -cyclooctadienyl complex [Pd(µ-Cl)(C 8 H 11 )] 2 (7). Complex 7 is an adequate precursor for the synthesis of other stable η 1 -allyl complexes, and no η 1 -η 3 allyl interconversion has been observed.

Three‐Way Cooperativity in d8 Metal Complexes with Ligands Displaying Chemical and Redox Non‐Innocence

“…However, for [2], the initial step is likely an oxidative addition to the Pd II center, whereby OTf À and HDMF + are added to the palladium center. Reductive elimination leads to the release of the ligand H 2 L. [9] The thus formed reactive complex containing a labile DMF ligand can react with unreacted [2] present is solution to generate the tetranuclear complex [4]. In compound [4], the O donors of L 2À act as a bridge between two Pd II centers (Scheme 3).…”

“…Reductive elimination leads to the release of the ligand H 2 L. [9] The thus formed reactive complex containing a labile DMF ligand can react with unreacted [2] present is solution to generate the tetranuclear complex [4]. In compound [4], the O donors of L 2À act as a bridge between two Pd II centers (Scheme 3). The detection of free H 2 L during the protonation of [2], as well as the known propensity of palladium to readily undergo oxidative-addition and reductive-elimination reactions lend support to the proposed mechanism.…”

“…Single crystals of the complexes [1], [2], [4], [5], and [6] suitable for diffraction studies were grown and used for X-ray diffraction studies (see the Experimental Section in the Supporting Information). Crystallographic details are listed in Table S1, and selected bond lengths and bond angles are given in Tables S2-S4 in the Supporting Information.…”

“…In the centrosymmetric tetranuclear Pd II complex [4], two of the Pd II centers are each bound to the O,N donors of the bridging L 2À ligand, and to a h 2 ,h 1 -coordinated cod ÀH ligand ( Figure 2). The other two Pd II centers are each bound to a triflato ligand and a cod ÀH ligand with the fourth coordination site being occupied by an O donor of L 2À , which bridges two Pd II centers.…”

Exploiting Non‐Innocent Ligands to Prepare Masked Palladium(0) Complexes

“…[9][10][11][12] These changes have been demonstrated to affect not only the rates of co-ligand dissociation, but also their intrinsic reactivity. [13,14] An unusual class of "responsive" NIL are the pyridyl-Nphosphinoimines 1, with the "open" bis(diisopropylamino) derivative 1 a existing in tautomeric equilibrium with a "closed" anellated iminophosphorane form 1 a' (Scheme 1). As a result, 1 a has been shown to behave as either a k 2 -PN or a k 1 -N ligand depending on the nature of the partner metal, and to exhibit unusual redox behavior.…”