Insertion reactions of platinum(II) ureylene complexes

Abstract

The reactivity of platinum(II) ureylene complexes towards various unsaturated molecules has been investigated. The complexes [Pt{NPhC(O)NPh}(cod)] 1a (cod = cycloocta-1,5-diene) and [Pt{NMeC(O)NPh}(cod)] 1b readily inserted phenyl isocyanate to give [Pt{NPhC(O)NPhC(O)NPh)}(cod)] and [Pt{NPhC(O)NMeC(O)NPh)}(cod)] respectively, with insertion taking place solely at the Pt–NMe linkage for the latter. When 1b was treated with the isoelectronic diphenyl carbodiimide the product was characterised as [Pt{NPhC(O)NMeC(O)NPh}(cod)], presumably the result of hydrolysis. The biureto ligand in the latter was readily liberated by hydrochloric acid to give N′-methyl-N,N″-diphenylbiuret. Complex 1b was also treated with various disubstituted acetylenes. Dimethyl acetylenedicarboxylate rapidly inserted into the Pt–NMe bond to give [Pt{C(CO₂Me)C(CO₂Me)NMeC(O)NPh}(cod)]. Compound 1b failed to react with diphenylacetylene, and was decomposed by methyl propiolate. Reaction of the more robust platinum ureylene [Pt{NMeC(O)NPh}(PPh₃)₂] with methyl propiolate displaced the urea dianion to give the diacetylide complex [Pt{CCC(O)OMe}₂(PPh₃)₂]. The compound [Pt{NMeC(O)NPh}(PPh₃)₂] was also treated with PhNSO and again the ureylene ligand was displaced to give the dimeric platinum sulfito complex [{Pt(SO₃)(PPh₃)₂}₂]·2PhNHC(O)NHMe. The crystal structure of the 2CHCl₃ solvate shows the complex to contain cocrystallised N-methyl-N′-phenylurea, hydrogen bonded from the NH moieties to the S(O)₂ groups. The compound presumably arises from hydrolysis of N-sulfinylaniline (or an intermediate insertion product thereof), and was also the only product characterised from the reaction of [Pt{NMeC(O)NPh}(PPh₃)₂] with sulfur dioxide. One of the chloroforms of crystallisation is also hydrogen bonded to the S(O)₂. The complex [Pt{NMeC(O)NPh}(PPh₃)₂] rapidly inserted carbon disulfide to give [Pt{S₂CNMeC(O)NPh}(PPh₃)₂] fully characterised by a single-crystal X-ray study. The complex contains a highly puckered six-membered ring, with the fold angle between the least-squares planes drawn through the co-ordination plane of the platinum and the remainder of the metallacycle being 56.8(1)°. In solution the compound slowly decomposes by loss of phenyl isocyanate to give [Pt(S₂CNMe)(PPh₃)₂], also fully characterised by an X-ray crystallographic study. All the complexes reported have been subjected to extensive ¹H, ¹³C and (where appropriate) ³¹P NMR analysis. Further data from electrospray mass spectrometry, IR spectroscopy and elemental analysis are also given.