Selective formation of 4-phosphanylated 1,2-dialkyl imidazole-2-thiones 3a-f has been obtained via a lithiation followed by phosphanylation reaction. The reactivity of 3a-f was examined towards oxidation and complexation reactions. All products were unambiguously characterized by elemental analyses, spectroscopic and spectrometric methods including X-ray analysis (3a, 3b, 4b, 4d, 5b, 6a and 6d).

1-Alkyl-3-methyl-4-diphenylphosphoryl-imidazolium hydrogensulfate (4a,b) (a: R(1) = R(2) = Me; b: R(1) = (i)Pr, R(2) = Me) and 1-alkyl-3-methyl-4,5-bis(diphenylphosphoryl)imidazolium hydrogensulfate (6a,c) (c: R(1) = (n)Bu, R(2) = Me) were obtained selectively and in good yields by oxidative desulfurization of 1-alkyl-3-methyl-4-diphenylphosphino-imidazole-2-thiones (2a,b) and 1-n-butyl-3-methyl-4,5-bis(diphenylphosphoryl)imidazole-2-thione (3c) or 1,3-dimethyl-4-diphenylthiophosphoryl-5-diphenylphosphino-imidazole-2-thione (5a), respectively, with hydrogen peroxide. Synthesis of phosphoryl functionalized imidazol-2-ylidene complexes of group VI metal pentacarbonyls (7a-9a) and (10b-12b) and bis(phosphoryl) functionalized imidazol-2-ylidene complexes of group VI metal pentacarbonyls (13c-15c) and (16a) with low steric demand (methyl, isopropyl, n-butyl) at both N-centers was achieved through deprotonation of imidazolium salts (4a,b) and (6a,c), respectively,-having HSO(4)(-) as a counterion-with potassium tert-butoxide followed by rapid addition of metal pentacarbonyl acetonitrile complexes [M(CO)(5)(CH(3)CN)] (M = Cr, Mo, W). The products were unambiguously characterized by elemental analyses, spectroscopic and spectrometric methods, and in addition, by single-crystal X-ray structure studies in the cases of 4b, 8a, 15c, and 16a; the latter two reveal imidazole ring bond distance alternation in contrast to 8a.

Metalation reactions were studied of a sterically demanding imidazole derivative, namely, 1-tert-butylimidazole (1), with different metalation reagents and subsequent reaction with diphenylchlorophosphane. The reaction product, 1-tert-butyl-2-diphenylphosphino-imidazole (2), was subjected to oxidation and complexation reactions to yield the corresponding products Ph(2)(Imi)P-E (E = O (3), S (4), Se (5), W(CO)(5) (8)) and in the case of borane-THF the N-BH(3) coordination product 10 was obtained. The analytical data of the new compounds are discussed, including X-ray diffraction studies of 3-5.

A synthetic route to C(4/5)-bis(phosphinoyl)imidazole-2-thiones (7d,e) (d: R(1) = (n)Bu, R(2) = Me; e: R(1) = n-dodecyl, R(2) = Me) and C(4/5)-bis(thio/selenophosphinoyl)imidazole-2-thiones (8b,c), (9a,b,e) and 10a (a: R(1) = R(2) = Me; b: R(1) = R(2) = Ph, c: R(1) = (i)Pr, R(2) = Me) is presented that employs initial C(5) lithiation of mono-phosphinoyl/thiophosphinoyl substituted imidazole-2-thiones (3c-e)/(4a-c,e) followed by reaction with chlorodiphenylphosphane, leading to mixed phosphinoyl and phosphanyl substituted imidazole-2-thiones (5c-e) or mixed thiophosphinoyl and phosphanyl substituted imidazole-2-thiones (6a-c,e). Subsequent oxidation of mixed phosphinoyl and phosphanyl substituted imidazole-2-thione (5d,e) with H2O2-urea gives the bis(phosphinoyl) substituted imidazole-2-thiones (7d,e), and the oxidation of mixed thiophosphinoyl and phosphanyl substituted imidazole-2-thione (6a-c,e) using H2O2-urea, elemental sulfur or elemental selenium gives a set of mixed P(V)-chalcogenide substituted imidazole-2-thiones (8b,c), (9a,b,e) and 10a, respectively. P(V,V) substituted imidazole-2-thiones 7d and 9a reacted with tellurium tetrachloride, titanium tetrachloride or palladium dichloride to give complexes 11d, (12d and 12d') and 14a, respectively, having a bidentate chelate (11d and 14a) or a monodentate bonding motif (12d,d'). The titanium complexes 12d,d' slowly and selectively converted into the mono-ethoxy substituted product 13 possessing a seven membered chelate motif being unprecedented in the titanium chemistry of phosphine oxide donor ligands. The compounds were characterized by elemental analyses, spectroscopic and spectrometric methods and, in addition, X-ray diffraction studies in the case of 5c, 7d, 8b, 9a and 13.

Herein, the synthesis and chemistry of P-functional tricyclic 1,4-dihydro-1,4-diphosphinines is described, following a recent communication on their use as precursors of 1,4-diphosphinines. In particular, ring formation of imidazole-2thione-based tricyclic 1,4-dihydro-1,4-diphosphinines 4a,b {-[P(Me 2 N)IMS R,R ] 2 -; IMS R,R = 1,3-dialkylimidazole-2-thione-4-yl}, first detected as side products, has been optimized to access 4d-f {-[P(Et 2 N)IMS R,R ] 2 -; IMS R,R = 1,3-dialkylimidazole-2-thione-4-yl}. The 1,4-dihydro-1,4-dichloro-1,4-diphosphinines 8a,b {-[P(Cl)IMS R,R ] 2 -; IMS R,R = 1,3-dialkylimidazole-2-thione-4-yl}, easily obtained from 4, are ideal starting materials for P-substituted products 9a-c (P-R; R = nBu, TMSC 2 -). The P-diorgano- [a] azole-2-derivatives, we recently described the first examples of tricyclic imidazole-2-thiones V having P-diethylamino groups ( Figure 1). [15] In the same short report, we also demonstrated a reductive conversion of P-Cl functional 1,4-dihydro-1,4-diphosphinines to give first examples of isolable 1,4-diphosphinines. [15] Following this short communication, we here report on detailed investigations on optimized synthetic protocols, as well as broad reactivity studies of P-functional tricyclic 1,4-dihydro-1,4-diphosphinines, to pave the way for their future use as unique ligands in coordination chemistry. Some reaction pathways and bonding situations have also been examined using DFT calculations. Results and DiscussionRecently, we demonstrated that backbone phosphanylation of imidazole-2-thiones allows access to acyclic dialkylaminobis(imidazole-2-thione-4-yl)phosphanes. [14] But in this study only imidazole-2-thiones with secondary or tertiary alkyl groups on either N-atoms (or at least on one) were used, and the final products were obtained in excellent yields without any byproducts. Interestingly, when 1,3-dimethyl imidazole-2-thione 1a, n-butyllithium, and dichloro(dimethylamino)phosphane 2a are used in THF, a white precipitate forms alongside the main product 3a (Scheme 1). The 31 P NMR spectrum shows the signal for the acyclic compound 3a (δ =14.4 ppm) and two resonance signals at δ = 9.8 and 10.2 ppm that are assigned to the cis and trans stereoisomers of 1,4-dihydro-1,4-diphosphinines 4a,a′ (ratio 1:1.3), according to the relative positioning of the P-NMe 2 groups. The trans isomer of 4a is easily isolated from the isomeric mixture by washing the precipitate with THF, because of the higher solubility of the cis isomer, and hence, it can be unambiguously characterized, possessing a 31 P resonance at NMR spectrum at 9.4 ppm (CDCl 3 ); the value is slightly upfieldshifted, compared with the reported derivatives IV (15.1-15.6 ppm [9] ).When the reaction is performed using 1,3-diethyl-imidazole-2-thione 1b, n-butyllithium and dichloro(dimethylamino)phosphane under the same conditions, a mixture of 3b and 4b is obtained (ratio 3:1), which is separable by column chromatography. The 31 P{ 1 H} NMR spectra of 3b and 4b (in CDCl 3 ) show similar chemical shifts as f...