Carbon-13 nuclear magnetic resonance study of the fluxional character of the .eta.6-(bicyclo[6.2.0]dodeca-2,4,6-triene)hexacarbonyldiiron(Fe-Fe) and a triethylphosphine derivative thereof, and the crystal structure of the latter

Abstract

The I3C N M R spectrum of the title compound (2) has been recorded at various temperatures from -120 to 102'. The four resonances for the eight-membered ring which are observed at room temperature broaden at -30' and are totally collapsed at about -85'; solubility problems precluded further study of these signals. The carbonyl carbon resonances were observed using enriched samples. The six-line spectrum expected from the crystal structure is observed at -120'. Four lines collapse and disappear into the base line between -120 and -88'. From -88 to -50' these four and one other signal reform into two signals of relative intensities 2:3. From ca. -50 to +102O the signal of intensity 2 and the previously unbroadened signal of intensity 1 collapse and re-form as a signal of intensity 3, while the signal of intensity 3 which was present at -50' sharpens. These changes can be understood in terms of a twitching process of the Fe2(C0)6 group relative to CioHl2 ligand followed by local averaging in one Fe(CO)3 group, followed by averaging within the other Fe(CO)3 group. No gliding motion or internuclear exchange of CO groups is allowed. The interpretation here is the same as that given previously for (CsHlo)Fe2(C0)6 (1). but the interpretation is more straightforward because there is less overlap of the three ppcesses. Moreover, by comparison of the slow exchange limit spectra of 1 and 2 a partial assignment can be made which is sufficient to allow an unequivocal determination that local scrambling occurs first about the allyl-bound iron atom. This point remained uncertain on the basis of data for 1 alone. The molecule (CioH12)Fe2(C0)5PEt3 was prepared and the position of the PEt3 ascertained by X-ray crystallography. From its I3C spectrum still further information is obtained which confirms all of the previous conclusions.Although the structural and dynamical properties of molecules of the general type 1-5 have been studied for a number of years, a complete and definitive understanding of their fluxional behavior has not yet been achieved.' The crystal structures of four of them, namely 1,2 2,3 3,4 and 55 about 12'. It has not yet been proved whether this C O scrambling occurs locally within each Fe(C0)3 group or involves passage of C O groups from one metal atom to the other, although there is indirect evidence favoring the former. It may also be noted that a 180' rotation of the entire t X = -CH,

Local and internuclear carbonyl scrambling in pentacarbonyl-7H-indenediiron (C9H8)Fe2(CO)5, and tetracarbonyl-7H-indene(triethylphosphine)diiron (C9H8)Fe2(CO)4(PEt3)

“…Fe(2) 0.28603 (6) 0.30003 (7) 0.30394 (6) 0.00328 (4) 0.00462 (5) 0.00447 (4) -0.00087 (8) 0.00012 (8) -0.00034 (9) 0(1) 0.4891 (3) 0.2825 (3) 0.1350 (4) 0.0058 (3) 0.0064 (3) 0.0086 (4) 0.0031 (5) 0.0027 (5) -0.0017 (6) 0(2) 0.2263 (3) 0.4591 (4) 0.0939 (4) 0.0053 (3) 0.0137 (5) 0.0075 (3) -0.0007 (6) --0.0040 (5) 0.0071 (7) 0(3) 0.4774 (4) 0.5838 (4) 0.0774 (4) 0.0091 (3) 0.0071 (3) 0.0086 (4) -0.0038 (6) 0.0066 (6) 0.0029 (6) 0(4) 0.3803 (4) 0.1223 (4) 0.2433 (6) 0.0059 (3) 0.0061 (3) 0.0175 (6) 0.0029 (5) 0.0029 (8) -0.0028 (8) 0(5) 0.1398 (3) 0.2549 (5) 0.1669 (4) 0.0051 (3) 0.0119 (4) 0.0083 (3) -0.0016 (6) --0.0035 (5) -0.0059 (7) C(l) 0.4466 (4) 0.3433 (5) 0.1686 (5) 0.0037 (3) 0.0052 (4) 0.0054 (4) 0.0009 (6) -0.0005 (6) -0.0008 (7) C(2) 0.2892 (5) 0.4526 (5) 0.1444 (5) 0.0043 (3) 0.0073 (4) 0.0045 (3) -0.0001 (7) 0.0005 (6) 0.0022 (7) C(3) 0.4439 (5) 0.5331 (5) 0.1343 (5) 0.0050 (3) 0.0046 (4) 0.0065 (4) 0.0005 (6) 0.0024 (7) -0.0003 (7) C(4) 0.3452 (4) 0.1959 (5) 0.2658 (6) 0.0033 (3) 0.0060 (4) 0.0088 (5) -0.0026 (6) --0.0006 (7) 0.0012 (8) C( 5 -0.0026 (6) --0.0031 (6) 0.0026 (7) C(10) 0.4797 (4) 0.4493 (5) 0.3471 (5) 0.0045 (3) 0.0053 (4) 0.0049 (4) -0.0020 (6) --0.0019 (6) -0.0012 (7) C(ll) 0.4272 (5) 0.5362 (5) 0.3377 (5) 0.0049 (3) 0.0058 (4) 0.0053 (4) -0.0015 (6) --0.0001 (6) -0.0036 (7) C( 12) 0.3333 (5) 0.5242 (5) Crystal Structure of (7H-C9H8)Fe2(CO)5. The positional Table II.…”

Diruthenium Carbonyl Complexes Bound to Guaiazulene: Preparation and Thermally Reversible Photoisomerization Studies of Phosphine and Phosphite Derivatives of (μ2,η3:η5-guaiazulene)Ru2(CO)5 and Iron Homologues

“…Hapticity change of conjugated π-ligands increases flexibility of their coordination modes, leading to high reactivity toward ligand exchange processes and other organometallic reactions. − The haptotropic rearrangement, which is one of the interesting outcomes of the hapticity change, is slipping of a transition metal fragment from one coordination site to the other with total electron count remaining intact on a polyaromatic hydrocarbon or cyclic polyene ligand. , Although a number of studies on the haptotropic rearrangement in mononuclear transition metal compounds bearing such ligands have been undertaken both experimentally and theoretically, , only a few reports have been published on the rearrangement of the dinuclear systems. − Diiron and diruthenium carbonyl complexes (μ 2 ,η 3 :η 5 -guaiazulene)M 2 (CO) 5 [M = Fe ( 1 ) and Ru ( 2 )] have two haptotropic isomers, 1-A and 1-B or 2-A and 2-B . Studies on CO scrambling processes were carried out by Cotton and co-workers in 1977, and the authors pointed out that thermal interconversion between those haptotropic isomers concomitantly took place 7a.…”

The carbonyl scrambling processes in the isomeric pentacarbonylguaiazulenediiron and homologous ruthenium molecules; a novel mechanism for the internuclear processes

“…Once an intermediate of the type I, II, or III is formed, at the relatively high temperature we are dealing with in step 2, scrambling of the CO groups in the Fe(CO)3 group (probably, but not necessarily, by rigid rotation) may be expected to occur rapidly. [19][20][21][22][23][24][25][26] Microscopic reversibility then demands that restoration of the initial structure occur only by one of the steps 1', I", or V". In this way each of the carbonyl groups, a, b, and c, has access to each of the three positions initially occupied by them whereas carbonyl group d can never stray from its initial site.…”