Oxidatively Induced P–O Bond Formation through Reductive Coupling between Phosphido and Acetylacetonate, 8-Hydroxyquinolinate, and Picolinate Groups

Abstract

The dinuclear anionic complexes [NBu4][(RF)2M(II)(μ-PPh2)2M'(II)(N(^)O)] (RF = C6F5. N(^)O = 8-hydroxyquinolinate, hq; M = M' = Pt 1; Pd 2; M = Pt, M' = Pd, 3. N(^)O = o-picolinate, pic; M = Pt, M' = Pt, 4; Pd, 5) are synthesized from the tetranuclear [NBu4]2[{(RF)2Pt(μ-PPh2)2M(μ-Cl)}2] by the elimination of the bridging Cl as AgCl in acetone, and coordination of the corresponding N,O-donor ligand (1, 4, and 5) or connecting the fragments "cis-[(RF)2M(μ-PPh2)2](2-)" and "M'(N(^)O)" (2 and 3). The electrochemical oxidation of the anionic complexes 1-5 occurring under HRMS(+) conditions gave the cations [(RF)2M(μ-PPh2)2M'(N(^)O)](+), presumably endowed with a M(III),M'(III) core. The oxidative addition of I2 to the 8-hydroxyquinolinate complexes 1-3 triggers a reductive coupling between a PPh2 bridging ligand and the N,O-donor chelate ligand with formation of a P-O bond and ends up in complexes of platinum(II) or palladium(II) of formula [(RF)2M(II)(μ-I)(μ-PPh2)M'(II)(P,N-PPh2hq)], M = M' = Pt 7, Pd 8; M = Pt, M' = Pd, 9. Complexes 7-9 show a new Ph2P-OC9H6N (Ph2P-hq) ligand bonded to the metal center in a P,N-chelate mode. Analogously, the addition of I2 to solutions of the o-picolinate complexes 4 and 5 causes the reductive coupling between a PPh2 bridging ligand and the starting N,O-donor chelate ligand with formation of a P-O bond, forming Ph2P-OC6H4NO (Ph2P-pic). In these cases, the isolated derivatives [NBu4][(Ph2P-pic)(RF)Pt(II)(μ-I)(μ-PPh2)M(II)(RF)I] (M = Pt 10, Pd 11) are anionic, as a consequence of the coordination of the resulting new phosphane ligand (Ph2P-pic) as monodentate P-donor, and a terminal iodo group to the M atom. The oxidative addition of I2 to [NBu4][(RF)2Pt(II)(μ-PPh2)2Pt(II)(acac)] (6) (acac = acetylacetonate) also results in a reductive coupling between the diphenylphosphanido and the acetylacetonate ligand with formation of a P-O bond and synthesis of the complex [NBu4][(RF)2Pt(II)(μ-I)(μ-PPh2)Pt(II)(Ph2P-acac)I] (12). The transformations of the starting complexes into the products containing the P-O ligands passes through mixed valence M(II),M'(IV) intermediates which were detected, for M = M' = Pt, by spectroscopic and spectrometric measurements.

Donor Behaviour of Anionic and Asymmetric Phosphanido Derivatives of Platinum and Palladium

“…A comparison of the 195 Pt chemical shifts of the starting materials (Pt 1 δ = ca. -3900 ppm, Pt 2 δ = -3450 to -3717 ppm for 1-4; [45,46] Pt 1 δ = -3821 ppm, Pt 2 δ = -3911 ppm for 5) with those of the adducts 1-5 shows that in all cases the addition of the [AgPPh 3 ] + group resulted in a strong deshielding of the 195 Pt centre, in accord with the donor behaviour of the Pt atoms in molecules with Pt-Ag bonds. As far as the picolinate complexes are concerned, the 195 Pt NMR signals of 6 were found (at 243 K) at δ = -3335 (Pt 1 ) and-3275 ppm (Pt 2 ), whereas the 195 Pt NMR signal of 7 was found (at 243 K) at δ = -3920 ppm (Pt 1 ).…”

“…The addition of [Ag(OClO 3 )(PPh 3 )] to CH 2 Cl 2 solutions of [NBu 4 ][(C 6 F 5 ) 2 Pt(μ-PPh 2 ) 2 M(hq)], [46] [NBu 4 ][(C 6 F 5 ) 2 -Eur.…”

“…In a few other cases, a very unusual 3c-2e interaction between the M II -(μ-P) bond of the phosphanido complex and the Ag I centre is formed [38,39] (the dinuclear fragment acts as a type D donor, Scheme 1). In some cases, the reaction proceeds either with the elimination of AgX (X = Cl, Br, C 6 F 5 ) from the palladium-and platinum-silver complexes [36,37,40,41] (Scheme 1, type E) or with the oxidation of the platinum(II) centre to plati-Pt(μ-PPh 2 ) 2 M(bq)], [45] [NBu 4 ][(C 6 F 5 ) 2 Pt(μ-PPh 2 ) 2 M-(pic)] [46] (M = Pt, Pd) and [NBu 4 ][(C 6 F 5 ) 2 Pt(μ-PPh 2 ) 2 -Pt(C 6 F 5 )(tht)] [47] results in the formation of the corresponding neutral adducts [(C 6 F 5 ) 2 Pt(μ-PPh 2 ) 2 (μ-AgPPh 3 sponding complexes, and Tables 1-6 list relevant bond lengths and angles. The six studied compounds are trinuclear PtMAg (M = Pt, Pd) complexes; however, although 1, 3, 4 and 5 display two M-Ag bonds and show a C-type structure (Scheme 1), complexes 6 and 7 do not display M-Ag bonds, and the ilver centre is bonded to one of the oxygen atoms of the picolinate ligand (Scheme 1, type G).…”

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Keywords: Metal-metal interactions / P ligands / Palladium / Platinum / Structure elucidation

The reactions of [Ag(OClO 3 )(PPh 3 )] F 5 )(tht)] (M = Pt, Pd; hq = 8-hydroxyquinolinate, bq = benzoquinolinate, pic = picolinate, tht = tetrahydrothiophene) afford the corresponding neutral adducts [(C 6 F 5 ) 2 Pt-(μ-PPh 2 ) 2 (μ-AgPPh 3 )M(bq)] (M = Pt, 1; Pd, 2), [(C 6 F 5 ) 2 Pt(μ-PPh 2 ) 2 (μ-AgPPh 3 )M(hq)] (M = Pt, 3; Pd, 4) [(C 6 F 5 ) 2 Pt(μ-PPh 2 ) 2 -(μ-AgPPh 3 )Pt(C 6 F 5 )(tht)] (5) and [(C 6 F 5 ) 2 Pt(μ-PPh 2 ) 2 M(pic-AgPPh 3 )] (M = Pt, 6; Pd, 7) as yellow solids. [36] In our experience, the results obtained so far in these types of reactions indicate that it is impossible to predict the behaviour of a particular complex towards Ag I .Recently, we have reported the reactions of I 2 with [NBu 4 ][(C 6 F 5 ) 2 Pt II (μ-PPh 2 ) 2 M II (C ∧ N)] [45] and [NBu 4 ]-[(C 6 F 5 ) 2 Pt II (μ-PPh 2 ) 2 M II (O ∧ N)] [46] [M = Pt, Pd; C ∧ N = benzoquinolinate (bq); O ∧ N = 8-hydroxyquinolinate (hq), picolinate (pic)], which contain dinuclear asymmetric anionic complexes and a chelate ligand. At room temperature, a dynamic process for the [AgPPh 3 ] + moiety, which passes from the top to the bottom part of the molecules 1-5, was ascertained.

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“…Recently, we have reported the reactions of I 2 with [NBu 4 ][(C 6 F 5 ) 2 Pt II (μ-PPh 2 ) 2 M II (C ∧ N)] [45] and [NBu 4 ]-[(C 6 F 5 ) 2 Pt II (μ-PPh 2 ) 2 M II (O ∧ N)] [46] [M = Pt, Pd; C ∧ N = benzoquinolinate (bq); O ∧ N = 8-hydroxyquinolinate (hq), picolinate (pic)], which contain dinuclear asymmetric anionic complexes and a chelate ligand. In all cases, the addition of molecular I 2 to the complexes resulted in oxidation of the metal centre and the formation of M II -M IV intermediates, which evolved through a PPh 2 /C ∧ N or PPh 2 / O ∧ N reductive coupling with the formation of new M II -M II compounds.…”