Cyanato complexes

Platinum(II) halides react with cyanate salts to give cyanato complexes. Reacting the compounds Pt(NCO)4 with triphenylphosphine gives Pt(NCO)2(PPh3)2.1628 These platinum(II) complexes are N-bonded. Treatment with carbon monoxide and alcohol yields the complex (172 equation 476).1629... 

Most frequently, the number of thiocyanate moieties in the extracted complex is equal to two, although some authors consider that the extracted species changes progressively to the trithio-cyanato complex (x = 1) and tetrathiocyanato complex (x = 0) on the successive extraction of a given aqueous phase.312 IR data show that the thiocyanate groups are bound to the metal via the nitrogen atom,315 as would be expected from the distinct A-character of zirconium(IV). 

It has been suggested that an adsorbed cyanato complex (NCO) exists on supported Ru catalysts under conditions of relatively high pressure, on the basis of transmission infrared experiments (67,68). However, no evidence for formation of such an intermediate, which is expected to have vibrational frequencies at 1150-1480 cm-1 due to the C-0 stretch, and at 2150- 2280 cm-1 due to the N-C stretch (46), was observed in the co-adsorption experiments on the Ru(001) surface. 

The marked difference in the stabilities of the copper and cadmium tetra-cyanato complexes serves as the basis for the separation of copper and cadmium ions (cf. Section 1.32). 

The CuCN(biL) complexes (biL = 2,2 -bipyridyl, 1,10-phenanthro-line) are monomeric in 2-aminoethanol, but their infrared spectra indicate that they may be di- or polymeric in the solid state there are no data available to elucidate the structures of the analogous thio-cyanato complexes 78, 328). 

The infrared spectra of a number of cyanato complexes are recorded in Table XIV. One of the compounds cp2M(OCN)2 (M = Ti,Hf) is incorrectly formulated. The infrared data are as listed, and N NMR [93) and mass spectral data [J45) support cp2Ti(OCN)2. However, the dipole moment ratios of the compounds suggest that they cannot both have the same type of coordination [422). Most cyanato complexes can... 

Table XIX gives some shift data for cyanate compounds, where a high-field shift is seen for JV"-cyanato complexes and a downfield shift observed for EtOCN (192). Similar arguments to those used for thiocyanate complexes presumably may be also applied here.

A number of metallocene cyanate complexes have been reported for these metals. Samuel (648) and Coutts and Wailes (219) reported cp2M(CNO)2 (M = Ti, Zr) independently in 1966. Samuel made no definite assignments of the structure, but Coutts and Wailes suggested the compounds were JV-cyanato complexes. Later, Burmeister et al. (145, 146) reexamined the compounds in more detail and argued that they, and the hafnium analog, were 0-cyanato complexes. This was... 

The homogeneous cyanato anions are presented in Table XLIII. Although the majority are iV-cyanato complexes, [Mo(OCN)3] , [Re-(0CN)g]2-, [Re(OCN)s]" (56), and [Hg(OCN)]4]= - (724) have been characterized by the positions of the fundamental cyanate vibrations only for the last compound has any confirmatory measurement been attempted, in which case NMR showed a relatively small upheld shift, characteristic for an N-bonded compound (192). 

In view of the foregoing situation and the uncertainties of whether or not O-cyanates do indeed exist or whether all the many A-cyanato complexes have been correctly characterized, any explanations concerning the behavior of the cyanate group would be premature. INDO calculations showed that almost equal electron densities existed at nitrogen and oxygen (383), so there is no apparent reason why both ends should not be involved in coordination. Attention has been drawn (86) to the fact that many of the metals found to form O-cyanates have vacant or only partly filled dn orbitals to interact with filled tt orbitals of the cyanate group. Whether these are centered on the oxygen or whether that atom forms the better a bond with these mostly class a metals remains to be seen. 

These facts, together with the remarkably few 0-cyanato complexes reported, suggest that the oxygen atom of the cyanate group is involved in coordination only with reluctance. Although there are obvious... 

The crystal standard of (7r-cp)2Ti(NCO)2 has been determined and confirms that, in the solid state, the cyanate group is here N-bonded it was only in the last stages of the analysis that the 0-bonded alternative could be finally eliminated (i). Hexa-iV-cyanato complexes of ytterbium, erbium, and neodymium have been reported as quaternary onium salts (16) and reference made to the series of tetraethylammonium salts of [Ln(NCO)0] (Ln = Eu-Yb) (22) these results extend Table XLII. The ESR spectra of series of complexes CuL2(NCO)2 (L = an, or substituted an) have been interpreted to show Cu— N(CO)—Cu bridges with no indication of any Cu-0 interactions (19). The ESCA spectra of [M(NCO)4] (M = Mn, Co, Zn) have been recorded (12). 

The preparation of the analogous cyanato complex, [Ru(NH3)4(NO)NCO]-(C104)2, is very similar KNCO is used in place of NaC2H302, and the complex cation is initially precipitated as the iodide salt, [Ru(NH3)4(NO)NCO]l2, salt A, from 2M KI solution. This iodide ion is displaced by filtering a solution of A into a saturated solution of NaC104. Salt A is identified from its infrared spectrum and elemental analysis. Anal. Calcd. for CH12N6O2I2RU N, 16.95 I, 51.20. Found N, 16.84 I, 50.32. 

Coordinated cyanamide does not add OH" to form the N-bound urea complex since it de-protonates 5.2) to ve the unreactive [Co(NCNH)(NH3)5p ion, but in acid it readily loses NH to form N-coordinated cyanate (equation 27). The analogous dimethylcyanamide complex cannot deprotonate and adds OH" to form urea (Scheme 21), but this does not proceed further to coordinated carbamic add and NHMCj in a process analogous to that suggested for the function of Ni in the metalloenzyme jack bean urease (which catalyzes the convemioo of urea to these products), nor does it lose NHMc2 to form the cyanato complex as suggested by Balahura and Jordan for the similar urea derivatives (equation 28). Alternatively, in acid solution the protonated urea rapidly isomerizes to the O-coordinated complex (r,/2 a 40 s, 25 °C Scheme 21). This isomer undergoes OH -catalyzed hydrolysis at the metal rather than at acyl carbon, so the function of the metalloenzyme has not been duplicated in this system. A similar property is found for 0-bound urea (equation 29). ... 

M —C N, cyano complex M—OCN. cyanato complex M—SCN, thiocyanato complex M—SeCN, selenocyanato complex... 

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