Copper(I) Complexes of Bis(2-(diphenylphosphino)phenyl)ether: Synthesis, Reactivity and Theoretical Calculations

The tricoordinated cationic Cu I complex [Cu( κ 2 - P , P' -DPEphos)( κ 1 - P - DPEphos)][BF 4 ] ( 1 ) containing a dangling phosphorus center was synthesized from the reaction of [Cu(CH 3 CN) 4 ][BF 4 ] with DPEphos in 1:2 molar ratio in dichloromethane. When complex 1 is treated with MnO 2 , elemental sulfur or selenium, the uncoordinated phosphorus atom undergoes oxidation to form P=E bond resulting in the formation of complexes of the type [Cu( κ 2 - P , P' -DPEphos)( κ 2 - P , E -DPEphos-E)][BF 4 ] ( 2 , E = O; 3 , E = S; 4 , E = Se) containing Cu-E bond. The zigzag polymeric Cu I complex [Cu( κ 2 - P , P' - DPEphos)(  -4,4'-bpy)] n [BF 4 ] n ( 5 ) was prepared by the reaction of [Cu(CH 3 CN) 4 ][BF 4 ] with DPEphos and 4,4'-bipyridine in equimolar ratio. The stereochemical influences of DPEphos on its coordination behavior are examined by DFT calculations.


Introduction
Mixed ligand Cu I complexes are of interest because of their luminescent properties, which find applications in construction of sensors and organic light emitting diodes (OLED). [1][2][3][4] In recent years, there has been several reports on mixed ligand complexes containing both bis(phosphines) and polypyridyls. 5,6 These complexes have been easily synthesized by treating bis(phosphines) with appropriate metal precursors followed by the addition of N-donor ligands. The mixed ligand systems consisting of both bis(phosphines) and partially functionalized or oxidized ligands are less extensive.
However, transition metal complexes containing a variety of dangling phosphorus ligands have been extensively studied. 7 Selective oxidation of one of the phosphorus centers in a bis(phosphine) using H2O2, MnO2, S and Se is very difficult since it always leads to the formation of a mixture of products, which complicates the isolation of the desired product. Often, Staudinger reactions of bis(phosphine)s with organic azides afford partially oxidized mono-phosphineimine derivatives in moderate yield. [8][9][10][11] Further, it is more challenging to synthesize a mixed ligand complex consisting of a bis(phosphine) and its mono-oxide derivative. In the last decade, there has been several reports on DPEphos ligand because of its potential applications in various organic transformation reactions. [12][13][14] Recently, we reported the synthesis of several ruthenium(II) complexes of DPEphos and its iminophosphorane derivative. 10,15 The DPEphos ligand showed several interesting coordination modes with Ru II center depending upon the bulkiness of other N, S and P donors. This investigation was aimed at exploring the reactivity of 3d metals such as Cu I towards DPEphos with considerable stereochemical influences which often produce coordinatively unsaturated yet moderately stable 16-electron complexes with wide catalytic applications. As a part of our research interest, 16  intensities in its 1 H NMR spectrum. The polymeric structure of complex 5 in the solid state is revealed by the X-ray structural results discussed below and presented in Figure   4.
All these complexes are obtained as colorless crystalline solids except the complex 5 which is yellow in color. The Cu I center in complex 1 adopts a distorted trigonal planar geometry, which is evident from the sum of the three P-Cu-P bond angles of 357.05°.
The uncoordinated dangling phosphorus center is oriented towards Cu I center at a distance of 3.958 Å which is considerably longer than the sum of van der Waals radii of Cu I and P (3.20 Å) 18  (2.2614(9), 2.2712(7) Å) (NN = 2,9-dimethyl-1,10-phenanthroline or 2,9-di-n-butyl-1,10phenanthroline). 5 The geometry around copper in complex 2 is pseudo-tetrahedral. The Cu1-P4,  As seen from and ΔEorbital in ΔEint for both the complexes. We note that the ΔEPauli term, which is responsible for the steric repulsion, is smaller for [Cu( 2 -P,P'-DPEphos)2] + due to its tetrahedral coordination and, hence, elongated PCu I distances, and that the attractive electrostatic interaction ΔVelec is more negative for [Cu( 2 -P,P'-DPEphos)( 1 -P-DPEphos)] + due to its significantly stronger PCu I interactions (see above). The orbital interaction terms are predicted to be comparable between the two systems.
The above analysis clearly demonstrates that the coordination of a Cu I center with four phosphorus atoms is, in principle, the energetically most favorable situation, but the entire energy gain will be lost in distorting the two DPEphos ligands to a geometry which facilitates such coordination. Hence, these results confirm that the observed difference in

Crystal Structure Determination
Single crystals suitable for X-ray diffraction of 1, 2, 4 and 5 were grown by slow diffusion of diethyl ether into dichloromethane solution and mounted on a glass fiber with epoxy resin. Unit cell determination and data were collected on Oxford Diffraction XCALIBUR-S CCD system using Mo Kα radiation (λ = 0.71073Å). The structures were solved and refined by full-matrix least-squares techniques of F 2 using the SHELX-97 (SHELXL program package). 34 The absorption corrections were done by multi-scan and all the data were corrected for Lorentz and polarization effects. The non-hydrogen atoms were refined with anisotropic thermal parameters. All the hydrogen atoms were geometrically fixed and allowed to refine using riding model.            )/w(Fo 2 ) 2 ]} 1/2 w = 1/ 2 (Fo 2 )+(xP) 2  where P = (Fo 2 +2Fc 2 )/3