Metathesis reactivity of bis(phosphinite) pincer ligated nickel chloride, isothiocyanate and azide complexes

Abstract

A series of nickel pincer complexes of the type [4-Z-2,6-(R 2 PO) 2 C 6 H 2 ]NiX (R = t Bu, i Pr, Ph; Z = H, CO 2 Me; X = NCS, N 3 ) have been synthesized from the reactions of the corresponding nickel chloride complexes [4-Z-2,6-(R 2 PO) 2 C 6 H 2 ]NiCl and potassium thiocyanate or sodium azide. X-ray structure determinations of these complexes have shown that the thiocyanate ion binds to the nickel center through the nitrogen. A comparable Ni-N bond length (approx. 1.87 Å for the isothiocyanate complexes and 1.91 Å for the azide complexes) and an almost identical Ni-C ipso bond length (approx. 1.89 Å) have been observed for these complexes. Metathesis reactivity of [4-Z-2,6-(R 2 PO) 2 C 6 H 2 ]NiCl and ligand exchange reactions between the nickel isothiocyanate and nickel azide complexes have been investigated. The metathesis reactions with thiocyanate/azide complexes are faster with a less electron rich and more sterically accessible nickel center. The thermodynamic stability of these nickel complexes has been rationalized using the hard-soft acid-base theory (HSAB theory); a harder ligand prefers a less electron rich nickel center. These © 2015. This manuscript version is made available under the Elsevier user license http://www.elsevier.com/open-access/userlicense/1.0/ 2 experimental results have been supported by quantum chemical analysis of the coordinating nitrogen atoms in SCNand N 3 -.

Application of POCOP Pincer Nickel Complexes to the Catalytic Hydroboration of Carbon Dioxide

“…The 1 H, 13 C{ 1 H} and 31 P{ 1 H} NMR spectra of 1c were in good agreement with the structure depicted in Scheme 2. Complex 1c showed the expected spectra characteristics for a POCOP pincer ligated nickel complex [14][15][16]27,[33][34][35][36][37][38][39][40][41][42]. Similar to other reported transition metal mercapto complexes [37,38,[43][44][45], the 1 H NMR resonance of the -SH proton of 1c appeared in a relatively high-field (−0.76 ppm) as a triplet.…”

“…As shown in Figure 1, the square-planar geometry for the Ni center of 1c is distorted; this is quite common for POCOP pincer nickel complexes [14][15][16]27,[33][34][35][36][37][38][39][40][41][42]. Both the C ipso -Ni and Ni-S bond lengths in complex 1c are comparable to those of the related pincer nickel mercapto complexes with t Bu 2 P or i Pr 2 P arms [37,38].…”

“…Complexes 1a [37], 1b [38], 2a-c [35] and 3a-c [35] were synthesized as described in the literatures. Complex 1c has never been reported before and was synthesized by the reaction between [2,6-(Ph 2 PO) 2 C 6 H 3 ]NiCl and NaSH in THF/methanol at room temperature (Scheme 2).…”

“…We have been interested in the chemistry of transition metal complexes bearing bis(phosphinite) (POCOP) pincer ligands [14,15,26,27,[33][34][35][36][37][38]. Recently, we applied some POCOP pincer nickel thiolato complexes, [2,6-(R 2 PO) 2 C 6 H 3 ]NiY (R = t Bu, i Pr; Y = SC 6 H 4 -p-OCH 3 , SC 6 H 4 -p-CH 3 , SPh, SC 6 H 4 -p-CF 3 , SCH 2 Ph), to the catalytic reduction of CO 2 with catecholborane (HBcat) [27].…”

The Reactivity of Mercapto Groups against Boron Hydrides in Pincer Ligated Nickel Mercapto Complexes

“…31 P and 11 B NMR spectra were referenced externally to 85 % H 3 PO 4 ( δ 0) and BF 3 ⋅Et 2 O ( δ 0), respectively. The starting pincer ligated nickel chloride complexes [2,6‐( t Bu 2 PCH 2 ) 2 C 6 H 3 ]NiCl, [2,6‐( t Bu 2 PO) 2 C 6 H 3 ]NiCl, [4‐MeOCO‐2,6‐( t Bu 2 PO) 2 C 6 H 2 ]NiCl and [2,6‐( i Pr 2 PO) 2 C 6 H 3 ]NiCl were synthesized according to the published procedures.…”