SYNTHESIS AND X-RAY STRUCTURE OF THE TETRANUCLEAR BUTTERFLY IRIDIUM CLUSTER IR4(CO)8L(MU-3-ETA-3-PH2PC(H)CPH)(MU-PPH2) (L=PCY3) AND C-13(H-1),H-1, AND P-31(H-1) NMR-STUDIES OF THE COMPOUNDS WITH L = CO, PCY3, AND P(OME)3

Deprotonation of HIr4(CO)10(mu-PPh2) (1) With DBU, which gives [Ir4(CO )10(mu-PPh2)]- (2), followed by reaction with Ph2PC=CPh and immediate protonation affords HIr4(CO)9(mu4-eta3-Ph2PC2Ph)(mu-PPh2) (3) and the novel species Ir4(CO)9(mu3-eta3-Ph2PC(H)CPh)(mu-PPh2) (4), in addition to the CO substitution products HIr4(CO)10-n(Ph2PC-CPh)n(mu-PPh2) (n = 1(5),2 (6)). Compound 4 undergoes facile CO substitution reactions w ith phosphines and phosphites (L) to yield Ir4(CO)8L(mu3-eta3-Ph2PC(H) CPh)(mu-PPh2) (L = PCy3 (7a), P(OMe)3 (7b), PPh3 (7c), PPhMe2 (7d)). T he derivative 7a has been structurally characterized by an X-ray diffr action analysis. Crystals of 7a are triclinic, space group P1BAR, with a = 12.626(1) angstrom, b = 20.405(5) angstrom, c = 12.493(2) angstro m, alpha = 94.16(2)-degrees, beta = 90.44(1)-degrees, gamma = 77.02(1) -degrees, V = 3128.0 angstrom3, Z = 2, and 2theta range 5-50-degrees, for 6698 measured reflections out of 6186 unique observed reflections (I0 > 2.0sigma(I0)); R = 0.04, R(w) = 0.04. The structure of 7a consis ts of a butterfly arrangement of metal atoms, whose wingtips are bridg ed by a PPh2 ligand, with the Ph2PC(H)CPh ligand interacting with a tr iangular metal face. The solution structures of compounds 4 and 7a,b h ave been investigated by a combination of variable-temperature H-1, C- 13{H-1}, and P-31{H-1} NMR studies, which have established that (i) 4 is isostructural with 7a,b, with a CO in place of L, (ii) 7a,b consist of two interconverting isomers in the ratio 3.9:1 at -20-degrees-C an d 1:5.9 at -60-degrees-C, respectively, and (iii) the structure determ ined by X-ray analysis is that of the major isomer of 7a, which is iso structural with the minor isomer of 7b.