Bis(2-pyridyl)phosphole 1 reacted with Cu(I) sources giving rise to dicationic or neutral dimers 2,3. In these derivatives, 1 acts as a 1kappaN:1,2kappaP:2kappaN donor with a symmetrically bridging P centre. X-ray diffraction studies of these species revealed no constraint due to the unusual coordination mode of the P donor. A comparative study with a monometallic Cu(I) complex in which 1 acts as a P,N chelate is presented. The acetonitrile ligands of the dicationic complex 2 can be displaced by a variety of donors. Bipyridine (bipy) acts as a chelating donor, while 1,1'-bis(diphenylphosphino)methane (dppm) and bis(2-pyridyl)phosphole 1 behave as bridging ligands. By using dppm and 1, the complexes arising from the stepwise displacement of the acetonitrile ligands of complex 2 can be isolated. X-ray diffraction studies performed on these novel complexes revealed that the P centre can easily switch from a bridging to a semibridging coordination mode. Of particular interest, within the same unit cell, complexes with P centres exhibiting bridging and semibridging coordination modes are observed. This switching can be induced by weak effects such as a different conformation of the incoming ligand. Cu(I) dimers assembled by 1 are air-stable derivatives that are not water sensitive. Hydrolysis of the PF(6) (-) counterion occurs under drastic conditions and results in the formation of a PO(2)F(2) fragment coordinated to a Cu(I)-1 fragment.

The recent discovery that tertiary phosphanes PR 3 can act as bridging ligands [1] (A, Figure 1) was a breakthrough in coordination chemistry, [2] since binucleating ligands potentially allow the synthesis of di-and polynuclear complexes that are of great interest in many fields, such as catalysis, bioinorganic chemistry, and materials sciences.[3] Up to now, only two types of binuclear compounds bearing symmetrically bridging phosphanes are known (Rh I [1] (C) and Pd I [4] homodimers (D), Figure 1). In order to establish phosphanes as versatile binucleating ligands, it is necessary to show that they can effectively stabilize other dinuclear fragments, and that they possess properties typical of well-established bridging ligands. [3] In this paper we describe the synthesis and characterization in the solid state of the first heterobimetallic complex and the first copper(i) homodimers bearing bridging phosphane ligands. Furthermore, we show that there is a continuum between symmetrically bridging (A) and semibridging (B) [5] coordination modes ( Figure 1), a key structural feature analogous to that observed for CO, [6] which is the archetypal bridging ligand.We have synthesized a heteronuclear Pd-Pt analog of complex D 1 (Figure 1) by a stepwise method, which allows the sequential introduction of the metal centers.[4b] Treatment of Pt II complex 1 with Pd 0 , 2,5-bis(2-pyridyl)phosphole (2), [7] and two equivalents of AgOTf gave derivative 3, which was isolated as an air-stable red powder (69 % yield, Scheme 1).High-resolution mass spectrometry data and elemental analyses are consistent with the proposed formula. Between room temperature and 173 K, the 31 P{ 1 H} NMR spectrum of 3 consists of a sharp singlet at d = 49.9 ppm ( 1 J P,Pt = 2113.5 Hz). As expected, two sets of signals are present for the pyridyl groups in the 13 C{ 1 H} NMR spectrum. [8] It is noteworthy that heterobimetallic 3 is stable in CH 2 Cl 2 solution for days; no signals corresponding to the Pd I dimer D 1 ( 31 P{ 1 H} NMR: d = 69.9 ppm) or to the corresponding, hitherto-unknown Pt I dimer are observed.The proposed structure of 3 was confirmed by an X-ray diffraction study (Figure 2).[8] The dication of 3 contains two square-planar metal centers capped by two 2,5-bis(2-pyridyl)phosphole ligands acting as six-electron m-1kN:1,2kP:2kN donors. The geometric parameters of the 2,5-bis(2-pyridyl)-phosphole ligands are almost identical for 3 and the corresponding homometallic Pd I dimer D 1 .[4] The metal-metal distance in 3 (2.7851 (9) ) is fairly long compared to typical Pd I ÀPt I single bond lengths, [9] but is similar to that measured for the dipalladium complexes D (2.767(1)-2.787(1) ).[4] The dication of 3 has a crystallographic center of symmetry at the midpoint of the metal-metal bond, which induces an equal occupancy of the Pd and Pt atoms at the two metal positions.[10] The metal-nitrogen bond lengths in 3 and D 1 are essentially equal, although the geometry of the M 2 P 2 core differs: for the homobimetallic complex D 1 the P ato...

The recent discovery that tertiary phosphanes PR 3 can act as bridging ligands [1] (A, Figure 1) was a breakthrough in coordination chemistry, [2] since binucleating ligands potentially allow the synthesis of di-and polynuclear complexes that are of great interest in many fields, such as catalysis, bioinorganic chemistry, and materials sciences.[3] Up to now, only two types of binuclear compounds bearing symmetrically bridging phosphanes are known (Rh I [1] (C) and Pd I [4] homodimers (D), Figure 1). In order to establish phosphanes as versatile binucleating ligands, it is necessary to show that they can effectively stabilize other dinuclear fragments, and that they possess properties typical of well-established bridging ligands. [3] In this paper we describe the synthesis and characterization in the solid state of the first heterobimetallic complex and the first copper(i) homodimers bearing bridging phosphane ligands. Furthermore, we show that there is a continuum between symmetrically bridging (A) and semibridging (B) [5] coordination modes ( Figure 1), a key structural feature analogous to that observed for CO, [6] which is the archetypal bridging ligand.We have synthesized a heteronuclear Pd-Pt analog of complex D 1 (Figure 1) by a stepwise method, which allows the sequential introduction of the metal centers.[4b] Treatment of Pt II complex 1 with Pd 0 , 2,5-bis(2-pyridyl)phosphole (2), [7] and two equivalents of AgOTf gave derivative 3, which was isolated as an air-stable red powder (69 % yield, Scheme 1).High-resolution mass spectrometry data and elemental analyses are consistent with the proposed formula. Between room temperature and 173 K, the 31 P{ 1 H} NMR spectrum of 3 consists of a sharp singlet at d = 49.9 ppm ( 1 J P,Pt = 2113.5 Hz). As expected, two sets of signals are present for the pyridyl groups in the 13 C{ 1 H} NMR spectrum. [8] It is noteworthy that heterobimetallic 3 is stable in CH 2 Cl 2 solution for days; no signals corresponding to the Pd I dimer D 1 ( 31 P{ 1 H} NMR: d = 69.9 ppm) or to the corresponding, hitherto-unknown Pt I dimer are observed.The proposed structure of 3 was confirmed by an X-ray diffraction study (Figure 2).[8] The dication of 3 contains two square-planar metal centers capped by two 2,5-bis(2-pyridyl)phosphole ligands acting as six-electron m-1kN:1,2kP:2kN donors. The geometric parameters of the 2,5-bis(2-pyridyl)-phosphole ligands are almost identical for 3 and the corresponding homometallic Pd I dimer D 1 .[4] The metal-metal distance in 3 (2.7851 (9) ) is fairly long compared to typical Pd I ÀPt I single bond lengths, [9] but is similar to that measured for the dipalladium complexes D (2.767(1)-2.787(1) ).[4] The dication of 3 has a crystallographic center of symmetry at the midpoint of the metal-metal bond, which induces an equal occupancy of the Pd and Pt atoms at the two metal positions.[10] The metal-nitrogen bond lengths in 3 and D 1 are essentially equal, although the geometry of the M 2 P 2 core differs: for the homobimetallic complex D 1 the P ato...