Butterfly complexes

Although apparently unrelated, some of the redox changes of these complexes are similar. In acetonitrile solution the OS4 complex undergoes a single-step two-electron oxidation [Ep — +0.78 V), which is coupled to fast coordination of solvent molecules according to the mechanismd  

As Fig. 14 testifies, the overall 60/62-CVE change induces opening of the OS4 tetrahedron to a butterfly arrangement. 

In a similar manner [H20s3Pt(CO)io P(C6Hn)3 ] can add two-electron donors L, such as CO or PPhs, to afford the 60-CVE butterfly-shaped complexes [H20s3Pt(CO)io P(C6H]i)3 (L)]. Fig. 15 shows the molecular structure of [H20S3Pt(CO) P(C6H )3 ].  

A series of homo- and hetero-nuclear 60-CVE alkynyl clusters of formula [M4(CO)io+ (RCsCR)] (M = Fe, Ru, Co) has been prepared. In their metallic 

The instability of the redox congeners of the C03M and RU4 complexes is due to decarbonylation reactions. Exhaustive one-electron reduction of [Co3Ru(CO)io-(PhC CPh)] in the presence of PPh3 affords the stable dianion [Co3Ru(CO)9-(PhC=CPh)] , and exhaustive two-electron reduction of [Ru4(CO)i2-(PhC=CPh)] affords the stable dianion [Ru4(CO)n(PhC=CPh)] The redox potentials of these electron transfers are reported in Table 8. 

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The Mn- Mn separations in both planar and butterfly complexes are very similar and range between 2.80 A and 3.45 A. The magnetic properties of these complexes have been studied extensively, and showed antiferromagnetic interactions between the manganese(III) centers. Electrochemical behavior of the butterfly conmlexes is summarized in Table 9 and both oxidative and reductive processes are observed. 

Table 10 Electrochemical properties for tetranuclear manganese(III)-carboxylato butterfly complexes.

Fig. 41. Molecular structure of [ (CO)5Fe2(jU.-Se2)2C(Ph)C(H)(jU.-dppe)] (129). [Reprinted with kind permission from Mathur, P. Hossain, M. M. Mahon, M. F. Carbon-selenium bond cleavage in the double butterfly complex [ (CO)6Fe2(jU.-Se)2)2(C(Ph)-C(H) ]. J Organomet. Chem. 1994, 471, 185. Copyright 1994 Elsevier Science S. A., P.O. Box 564, 1001 Lausanne, Switzerland.]...

The Pauson-Khand reaction gives the same product as the group 4 metal-mediated reductive coupling and carbonylation, and both reactions proceed by essentially the same mechanism formation of an alkyne-metal tt complex, insertion of an alkene, insertion of CO, and reductive elimination. Some details differ, however. When an alkyne is added to Co2(CO)g, CO evolves, and an isolable, chromatographable alkyne-Co2(CO)6 complex is obtained. This butterfly complex contains four Co(II)-C bonds, and the Co-Co bond is retained. The formation of the alky n e-C o2 (C O) 6 complex involves the formation of an ordinary tt complex of the alkyne with one Co(0) center, with displacement of CO. The tt complex can be written in its Co(II) cobaltacyclopropene resonance structure. The tt bond of the cobaltacyclopropene is then used to form a tt complex to the other Co center with displacement of another equivalent of CO. This second tt complex can also be written in its cobaltacyclopropene resonance structure. The alkyne-Co2(CO)6 complex has two 18-electron Co(II) centers. 

As the cleavage of the first P-P bond to yield P4-butterfly complexes has extensively been discussed in the previous sessions, we will now skip to illustrate those polyphosphorus ligands formed via rupture of a second bond in the tetraphosphorus tetrahedron. 

The routines, given later, have been written in Microsoft BASIC and use arrays to store the calculated parameters. In these subroutines, the variables CO and NALPHA are given by Nf3 /3k and x(TIP) (temperature-independent paramagnetism), respectively. These subroutines can be used in conjunction, for instance, with a spreadsheet to quickly work out a new system or to check out one in the literature. As an example of the latter, we take a very recent case of rhomboidal symmetry found by Chaudhuri et al. (54) in a butterfly complex in which the body ions are Mn with Sj = S3 = 2, and the wing-tips are Cr , with S2 = S4 = f. The lowest two coupled states found for best fit and given in Fig. 4 of Chaudhuri et al. (54) are 3, 3, 0) (ground) and 2, 3, 1) separated by 15.8 cm Use of Eq. (10) shows the following ... 

At low temperature, platinum clusters 20 react with [Ir(CO)4] to give, via GO loss, butterfly complex 55. One carbonyl ligand in 55 can be displaced by triphenylphosphite giving 56 (Scheme 12), the X-ray structure of which clearly shows a butterfly structure with iridium at a wingtip position. Complex 55 is thermally unstable, and is shown... 

Reaction between Rus(/r5-C)(CO)is and 2,2 -bipyridyl (bipy) in the presence of Mc3NO affords the wingtip-bridged butterfly complexes Ru5(/tts-C)(CO)i4(77 -bipy) 43 and Rus(/r-H)(/rs-C)(/r-77 -N2CioH7)(CO)i3 44, the latter being the orthometallated derivative of the former. Reaction with 1,10-phcnanthrolinc (phen) affords the analogous complexes 45 and Ru5(/i-H)(/tt5-C)(/r-77 -phen-H)(CO)i3. ... 

Reaction of Ru3(CO)i2 with ethyl methacrylate affords the edge-bridged butterfly complex Rus(/t-H)2 /t4-CC-MeC(0)0Et (C0)i4 57. A series of clusters with nuclearities between 4 and 7 are formed from the reaction of... 

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