Formation of an imidazoliumyl-substituted [(L(C))(4)P(4)](4+) tetracation and transition metal mediated fragmentation and insertion reaction (L(C) = NHC)

Tetracationic cyclo-tetraphosphane [(L(C))(4)P(4)](4+) as triflate salt (3[OTf](4)) (L(C) = 4,5-dimethyl-1,3-diisopropyl-imidazol-2-yl) is obtained in high yield from the reduction of [L(C)PCl(2)](+) (4[OTf]) with 1,4-bis(trimethylsilyl)-1,4-dihydropyrazine (6) and represents the first salt of the cationic cyclo-phosphane series with the general formula [L(n)P(n)](n+). Theoretical calculations reveal the electrophilic nature of the P atoms within the P(4)-ring due to the influence of the imidazoliumyl-substituents. Further reduction of 3[OTf](4) with 6 affords the unexpected formation of the notricyclane P(7)-type cation [(L(C))(3)P(7)](3+) (9[OTf](3)). Selective transition metal mediated [2 + 2]-fragmentation of 3(4+) is achieved when 3[OTf](4) is reacted with Fe(2)(CO)(9), Pd(PPh(3))(4) and Pt(PPh(3))(4) leading to the formation of the dicationic diphosphene complexes [(η(2)-L(C)P[double bond, length as m-dash]PL(C))Fe(CO)(4)](2+) (12[OTf](2)) and [(η(2)-L(C)P[double bond, length as m-dash]PL(C))M(PPh(3))(2)](2+) (13[OTf](2) for M = Pd; 14[OTf](2) for M = Pt). In contrast, the reaction of 3[OTf](4) with an excess of AuCl(tht) gives rise to the formation of the five-membered ring complex [((L(C))(4)P(4))AuCl(2)](3+) (15[OTf](3)), where the Au(i) atom reductively inserts into a P–P bond of 3(4+).