Structural diversity in Cu(i) complexes of the PNP ligand: from pincer to binuclear coordination modes and their effects upon the electrochemical and photophysical properties

Abstract

A set of new copper(i) complexes is synthesized and characterized using a labile PNP pincer ligand (PNP = N,N'-bis(diphenylphosphine)-2,6-diaminopyridine). A homoleptic Cu(i) complex [Cu(PNP-κP:κN)], (1), was prepared, and taking advantage of the uncoordinated phosphorus atoms in (1), reaction with a second Cu(i) atom bearing secondary ligands (PPh, phen or dmp) allows the formation of new complexes: a bimetallic helicate [Cu(PNP)(phen)], (2), a mononuclear pincer complex [Cu(PNP)(PPh)], (3), and a heteroleptic complex [Cu(PNP)(dmp)], (4). All complexes were characterized by X-ray crystallography, NMR (VT-NMR for (1) and (4)), cyclic-voltammetry, and steady-state and time-resolved luminescence spectroscopy. The fluxional behavior in (1) was studied by P VT-NMR, where an E value of 47.42 kJ mol was calculated for the intramolecular alternating coordination of -PPh moieties in PNP to the metal atom. This set of compounds reveals the versatility of the PNP ligand when added to the coordinating properties of Cu(i). The four complexes exhibit emission in solution and complexes (2)-(4) display intense luminescence in the solid state. The oscillographic traces showing the decay of the luminescence were fitted to biexponential functions with time constants: 8.0 μs > τ > 0.37 μs and 50 μs >τ > 2.2 μs for complexes (2), (3) and (4), respectively. Radiative relaxation is associated with electronic transitions in both the ligand PNP and metal-to-ligand charge transfer (MLCT).

[Cu(POP)(N^S)][PF6] and [Cu(xantphos)(N^S)][PF6] compounds with 2-(thiophen-2-yl)pyridines

“…[Cu(POP) ( 13 13 C{ 1 H} NMR (126 MHz, acetone-d 6 ) d/ ppm 159.4 (C A6 ), 158.5 (C C1 ), 152.9 (C A2 ), 143.7 (C B2 ), 139.8 (C A4 ), 135.2 (C C3 ), 134.1 (t, J PC ¼ 8 Hz, C D2 ), 133.5 (C C5 ), 131.5 (C D4 ), 130.9 (C D1 ), 130.7 (C B4 ), 130.0 (t, J PC ¼ 5 Hz, C D3 ), 128.0 (C B3 ), 127.8 (C B5 ), 126.1 (C C4 ), 124.3 (C A5 ), 123.6 (C C2 ), 121.2 (C C6 ), 119.9 (C A3 ), 24.9 (C Me ). 31 36.6 (C xanthphos bridge ), 28.9 (C Me a ), 25.1 (C Me-A6 ).…”

“…31 ). 13 C{ 1 H} NMR (126 MHz, acetone-d 6 ) d/ppm 158.6 (C A6 ), 155.1 (t, J PC ¼ 6 Hz, C C1 ), 152.8 (C A2 ), 142.9 (C B5 ), 140.5 (C B2 ), 140.0 (C A4 ), 134.8 (t, 31…”

“…10 A few copper(I) complexes with a P 2 N 2 donor set generated from two P^N ligands containing a pyridine with an appended phosphorus moiety have been reported. [11][12][13][14][15][16][17] In an effort to broaden the scope of emissive copper(I) coordination compounds, we decided to investigate N^S donor ligands as an alternative hard-so combination.…”

Redox Instability of Copper(II) Complexes of a Triazine‐Based PNP Pincer

“…[2][3][4][5][6][7] Amongst them, pincer ligands with a PNP motive have recently attracted attention. [8][9][10][11][12][13][14][15] Typical ligands of this type were the well-studied N,N'-bis(diaryl/alkylphosphino)-2,6-diaminopyridines [2,[7][8][9][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] (PNP NpyR -R', Scheme 1A), 2,6-bis((diaryl/ alkylphosphino)methyl)pyridines (PNP CpyR -R', Scheme 1B), [3,[5][6][7][8][9][10][11]14,15,[30][31][32][33][34][35] the N,N'-bis(diaryl/alkylphosphino)-2,6...…”

“…[25] Frequently, the deprotonated ligands *PNP NTR -R' were reported to be important for the catalytic transformations. [30][31][32][33][34][35][36][37][38][39]47] Although Cu(I) and Cu(II) complexes of N,N'-bis(diaryl/ alkylphosphino)-2,6-diamino-pyridine ligands (PNP NpyR -R'; R = H; R'=iPr, tBu, Ph) were reported, [13,17,27,29,[47][48][49] no Cu complexes of the 1,3,5-triazine derivatives (PNP NTR -R') were known to date. In a very recent report Bedford et al describe the intrinsic instability of the much related Cu(II) complex [Cu(PNP Npy -Ph)(OAc) 2 ] (PNP Npy -Ph = N,N'-bis(diphenylphosphino)-2,6-diamino-pyridine) to undergo Cu(II) reduction to Cu(I) and oxidation of the phosphine moieties in the presence of water, [48] disagreeing with earlier claims that the Cu(II) complex is an effective catalyst in Suzuki type coupling reactions.…”