Platinum(II) phosphine complexes of dicarboxylates and ammonia: crystal structures of [{Pt(PPh3)2}2{µ -1,3-(O2C)2C6H4}2], [{Pt(PPh3)2(NH3)}2{µ-1,4-(O2C)2C6H4}][PF6]2and cis-[Pt(PPh3)2(NH3)2][NO3]2

Abstract
The reaction of [Pt(PPh 3 ) 2 (CO 3 )] with a rigid dicarboxylic acid H 2 L gave rise to dimeric compounds [{Pt(PPh 3 ) 2 } 2 (µ-L) 2 ] 1 [H 2 L = C 6 H 4 (CO 2 H) 2 -1,4 (terephthalic acid) a, C 6 H 4 (CO 2 H) 2 -1,3 (isophthalic acid) b, trans,trans-HO 2 CCHCHCH CHCO 2 H (muconic acid) c or 4,4′-HO 2 CC 6 H 4 C 6 H 4 CO 2 H (biphenyldicarboxylic acid) d], which have been characterised spectroscopically and, in the case of 1b, crystallographically. When the reaction was carried out in the presence of NH 4 PF 6 the NH 4 + competed with the carboxylic acid and the major product from the reaction was [{Pt(PPh 3 ) 2 (NH 3 )} 2 (µ-L)][PF 6 ] 2 2, which has been characterised crystallographically for L = terephthalate. This suggests that NH 4 + is acidic enough to react with [Pt(PPh 3 ) 2 (CO 3 )], which has been confirmed by the synthesis of cis-[PtL 2 (NH 3 ) 2 ]X 2 [L = PPh 3 , X = PF 6 3a or NO 3 3b; L = PEt 3 , X = PF 6 4a or NO 3 4b; L 2 = Ph 2 PCH 2 CH 2 PPh 2 (dppe), X = PF 6 5a] from [PtL 2 (CO 3 )]. The complex cis-[Pt(PPh 3 ) 2 ( 15 NH 3 ) 2 ][NO 3 ] 2 was synthesized from 15 NH 4 NO 3 and characterised by a combination of 31 P-{ 1 H}, 15 N-{ 1 H}, 195 Pt and 1 H NMR spectroscopy. The crystal structure of cis-[Pt(PPh 3 ) 2 (NH 3 ) 2 ][NO 3 ] 2 3b has been determined and shows strong hydrogen bonding between the co-ordinated ammonia and the nitrate counter ions. The compound PhC 2 CO 2 H also reacted with [PtL 2 (CO 3 )], though the products were not the expected bifunctional carboxylates cis-[PtL 2 (O 2 CC 2 Ph) 2 ] but the bis(phenylalkynyl) compounds cis-[PtL 2 (C 2 Ph) 2 ] (L = PPh 3 6, L 2 = dppe 7).

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