Palladium complexes thiocyanate

Reaction of the diphosphines Ph2P(CH2) PPh2 (n = 1-3) with MCl2(PhCN)2 affords 1 1 m-complexes (Figure 3.46) [102]. (Note the use of the labile PhCN adducts if the MCl salts are used, Magnus type compounds M(P-P)2+MCl4- are formed.) Similar complexes are formed with other halides for the thiocyanates see section 3.8.6. The structures of the palladium complexes have been determined (Table 3.10) with square coordination only achieved for n = 3 with the formation of a six-membered metal-chelate ring. 

Most of the studies of ambidentate behaviour among thiocyanates concern palladium complexes a recent report [129], however, investigated Pt(bipy)(NCS)2... 

Tabic 1 Typical Palladium(II)-Thiocyanate and -Selenocyanate Complexes and IR Data ... 

Burmeister and colleagues have described the related pseudohalogen derivatives MfterpyjXj (X = SCN or SeCN) (90-92). The platinum compound exhibits the two thiocyanate stretching frequencies expected for a square-planar complex, and is formulated [Pt(terpy)(NCS)][NCS], However, the palladium complexes are less easily formulated, exhibiting absorptions due to coordinated ECN (E = S or Se) only. These observations were interpreted in terms of a square-planar structure, with a bidentate terpy ligand in view of the known ability for palladium and platinum diimine complexes to form five-coordinate species, this formulation must also be considered. In the absence of definitive structural evidence, the formulation as five-coordinate species must be regarded as speculative. 

Some Mixed-Ligand Complex Thiocyanates or Palladium(II) and Platinum(II)... 

Some five-coordinate palladium(II) thiocyanate complexes have been reported. Both [Pd(2,9-diMe-phen)2SCN]C104 (606) and [Pd(o-Me2As-C6H4)3As(NCS)]NCS (375) have been characterized, but the mode of coordination is unspecified in [PdL2CNS]NCS [L = 1,8-naphthylenebis-(dimethylarsine)] (636) in the latter system, six coordination seems to occur in solution (636). 

Fig. 12.46 Structures of four palladium complexes illustrating combined steric and electronic effects on bonding of the thiocyanate ligand. [From Palenik, G. J. Steffen, W. L. Mathew, M. Li, M. Meek, D. W. Inorg. Nucl. Chem. Leu. 1974. 10, 125-128. Reproduced with permission.]...

The required C3S unit also exists in 2-thio derivatives of benzoic acid. Thus, thionation of diphenyl disulfide-2,2 -dicarboxylic acid gives benzo-l,2-dithiole-3-thione (37b). This approach can be also applied to thienodithioles and to dithiolopyridines <82AHC(3l)63>. In a conversion of thiosalicylic acid to benzo-l,2-dithiole-3-thione, the extra sulfur atom is provided by thiolacetic acid <920PP488>. The necessary units also appear in some palladium complexes, which by treatment with thiocyanate give benzo-l,2-dithiolium salts and other fused dithioles (Equation (10)) <90JCS(Pl)288l>. 

Temperature-dependent luminescence spectra for a series of palla-dium(ii) and platinum(ii) complexes with thiocyanate, halide, and dithiocarbamate ligands have been investigated. The results show that the luminescence band maxima of palladium(ii) and platinum(ii) complexes have opposite shifts with increasing temperature. The palladium complexes exhibit a negative shift of at least 1 cm /K, while the platinum(ii) ones have a positive shift of -1-1.6 cm /K. ... 

M-SCN-M bridges absorb well above 2100 cm (below 4.76 pm). Thiocyanates acting as bridging groups in platinum and palladium complexes absorb in the region 2185-2150cm (4.58-4.65pm) (see Table 22.20). 

Arsonium salts have found considerable use in analytical chemistry. One such use involves the extraction of a metal complex in aqueous solution with tetraphenyiarsonium chloride in an organic solvent. Titanium(IV) thiocyanate [35787-79-2] (157) and copper(II) thiocyanate [15192-76-4] (158) in hydrochloric acid solution have been extracted using tetraphenyiarsonium chloride in chloroform solution in this manner, and the Ti(IV) and Cu(II) thiocyanates deterrnined spectrophotometricaHy. Cobalt, palladium, tungsten, niobium, and molybdenum have been deterrnined in a similar manner. In addition to their use for the deterrnination of metals, anions such as perchlorate and perrhenate have been deterrnined as arsonium salts. Tetraphenyiarsonium permanganate is the only known insoluble salt of this anion. 

Chelate complexes could only be prepared in the case of platinum(II) as the metal ion, while the group V atom alone acted as a donor toward palladium(II) and mercury(II). The coordinated olefin in the chelate complexes was found to be readily displaced by monodentate ligands such as tertiary arsines, -toluidine and the thiocyanate ion. It was suggested by these workers that chelation would take place more readily if the olefinic phosphine or arsine were subject to greater steric restrictions than was the pentenyl ligand. 

The heterobinuclear complex [PdPtCl2( -dppm)2] can also be prepared by treating the product from the reaction of dppm and [Pd(PPh3)4] with [PtCl2(NCBu,)2].76 The corresponding bromide, iodide and thiocyanate dipalladium and palladium-platinum complexes have been prepared by metathesis of the dichloride (9) with NaX.76... 

P NMR spectroscopy.53 Steric factors account for the different coordination modes, while the influence of electronic factors is evidenced by the difference in structure between analogous palladium(II) and platinum(II) compounds, for example, the thiocyanates are N- and S-bonded in [Pd(NCS)(SCN)(diars)], but only S-bonded in [Pt(SCN)2(diars)].54 These and other diphosphine or diarsine complexes of palladium(II) with thio- or seleno-cyanate ligands are further discussed in Section 51.8.2.6. 

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