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2-(MeR 1 CCR 2 )-and 2-(CH 2 CR 1 CH 2 CH 2 )-pyridine (R 1 ,R 2 = H or Me) undergo 1,2-double-bond shifts and 2-(CH 2 CHCH 2 CH 2 CH 2 )-pyridine undergoes a 1,3-double-bond shift on displacement of norbornadiene from [M(CO) 4 norb] (M = Cr, Mo or W) to give complexes of the type [M(CO) 4 LL'] (LL' = 2-(allyl)or 2-(substituted allyl)-pyridine), which do not exhibit conformational isomerism involving the plane of the coordinated olefin.

Direct 103Rh n.m.r. studies on [Rh4(CO)12–xLx][L = P(OPh)3, x= 1–4] at low temperatures support the solution structures previously proposed and, although the apical rhodium resonance always occurs at lowest frequency, there is little variation in δ(103Rh) with increasing ligand substitution. Measurements of 13C-{103Rh} allow unambiguous assignment of the 13C n.m.r. spectra when x= 1 and 3 and δ(13COax) is always at lowest frequency with 1J(103Rh–13COax)≃1J(103Rh–13COap) < 1J(103Rh–13COrad); this suggests a new assignment for the 13C n.m.r. spectrum of [Rh4(CO)12].

13C-{103Rh} NMR measurements on [Rh12(CO)30]2{3} at {3}72°C show that the structure in solution is consistent with that found in the crystalline state.

195 Pt n.m.r. data are reported for [Ptn(CO)2n]2–(n= 3, 6, or 9) and, when n= 9, the spectra are consistent with rotation of the outer Pt3-triangles with respect to the middle triangle about the principal 3-fold axis; inter-exchange of Pt3-triangles occurs in mixtures of [Pt9(CO)18]2– and [Pt12(CO)24]2– at 25°C.

31 P N.m.r. spectra show that addition of an equimolar amount either of bromine to trans-[PtCl2(PR3)L](R = Et, L = py, 3,5-Me2-py, 4-But-py, PEt3; R = Bun, L = py)(py = pyridine) or of trans-[PtCl4(PEt3)(py)] to trans-[PtBr4(PEt3)(py)] results in halogen scrambling and gives an approximately statistical distribution of trans-[PtBrxCl4–x(PEt3)L](x= 0–4).

13 C n.m.r. studies on the three structurally related carbonyl clusters [Rh6(CO)16], [Rh6(CO)15]2– and [Rh7(CO)16]3– show that [Rh6(CO)16] is not fluxional at +70°, [Rh6(CO)15]2– readily undergoes intra-carbonyl exchange at –70° and [Rh7(CO)16]3– is not fluxional at –70° but undergoes partial intra-exchange at +25°.

Variable-temperature multinuclear n.m.r. studies (13C, 13C-{l03Rh}, 13C-{31P}, and 3lP) are reported for [Rh9E(C0)21]2-, [Rhl0E(C0)22]3- (E = P or As), and [Rh12Sb(C0)27]3-. In all cases, complete fluxionality of both the carbonyl and metal polyhedra are observed at high temperatures, and at low temperatures it has been possible to obtain spectra for the Rh9 and Rhl0 clusters, which are fully consistent with their solid-state structures, thus allowing a complete spectroscopic assignment ; the Rhl2 cluster is still fluxional in solution at -97 °C.

Metallation of 2-vinylpyridine, (vpy), occurs on reaction with [Rh2X6(PBun3)4](X = Cl or Br) to give [[graphic omitted]HCH)py}X2(PBun3)2], which undergoes an unusual substitution reaction with bromine to give [[graphic omitted]HCBr)py}Br2(PBun3)2].

Die Reaktion von K,[Co6 (CO) ,5 ] mit NOBF4 in THF liefert eine Mischung aus Co(II), Co(CO)3NO, Spuren von Co4(CO)" und dem neuen Anion [Co6N(CO),5 1′, das mit 40-50% Ausb. als K-Salz abgetrennt wurde.

Carbon-13 n.m.r. spectra, over a range of temperature, are reported for [Ni5(CO)12]2–, [Ni6(CO)12]2–, [Ni9(CO)18]2–, and [Ni12(CO)21H4–x]x–(x= 2 or 3). At –80 °C the spectra of [Ni6(CO)12]2–, [Ni9(CO)18]2–, and [Ni12(CO)21H2]2– are consistent with their solid-state structures; terminal–bridge carbonyl exchange is observed at higher temperatures with the lowest-energy process involving exchange on the outer metal triangles. Similar behaviour is found for [Ni12(CO)21H]3– and in addition H migration may occur. Spectroscopic and chemical evidence is presented for the formation of a new cluster, [Ni7(CO)15]2–, and its fluxional behaviour is reported. At 60 °C [Ni12(CO)21H2]2– is transformed cleanly into [Ni9(CO)18]2– whereas [Ni12(CO)21H]3– does not react under the same conditions.

A combination of variable-temperature, multinuclear n.m.r. studies (1H, 13C, 103Rh, 1H-{103Rh}, and 13C-{103Rh}) has allowed the ligand (CO/H) migrations in [Rh13(CO)24Hn](5 –n)–(n= 1–4) and [Rh14(CO)25HX](4 –x)–(x= 0 or 1) to be established. In both types of compound, interstitial H migration is found at room temperature with complete randomisation of carbonyls in the Rh14 clusters and partial migration of carbonyls in the Rh13 clusters; in neither case is there evidence for rearrangement of the metal polyhedron. At low temperatures (–90 °C), H migration still occurs in [Rh14(CO)25H]3– but not in [Rh13(CO)24H3]2– and [Rh13(CO)24H2]3– which have the same structural features as found in the solid state with the hydride ligands occupying pseudooctahedral holes in the metal skeleton. All the values of δ(103Rh) for the interstitial rhodium atoms are at significantly higher frequency than the values for the surface rhodium resonances and shift significantly to lower frequency with increasing interstitial hydride content.

The use of multinuclear magnetic resonance studies to obtain information on structures, bonding and mechanisms of ligand and/or metal rearrangements for carbonyl clusters in solution will be illustrated. There has been a rapid increase in both the variety (different metal polyhedral geometries and different combinations of metals/interstit ial elements) and size of transition metal clusters during the last 15 years with some of the highest nuclearity clusters now of the size (> 40 metal atoms) of small metallic crystallites (z. 10 8). part due to the developing preparative expertise of different research groups and also to the improvements in instrumentation, particularly X-ray diffraction and multinuclear magnetic resonance, which are necessary for their characterisation .

Two crystal species, [NMe4]3[Rh11(CO)23]·Me2CO (1) and [NMe4]3[Rh11(CO)23]·C6H5Me (2), containing two isomers of the same anion, have been isolated and investigated. The salt (1) crystallizes in the monoclinic space group P21/n, with a= 12.275(4), b= 19.987(5), c= 24.007(5)A, β= 104.47(3)°, and Z= 4; the salt (2) gives monoclinic crystals, space group P21/c, with a= 19.545(2), b= 12.597(2), c= 24.151(2)A, β= 92.62(1)°, and Z= 4. The structures were solved and refined on the basis of 7 421 [(1)] and 3 531 [(2)] significant counter data, converging to final R values of 0.032 and 0.041, respectively. The metallic skeleton (of ideal D3h symmetry) is the same in the two species, based on three face-to-face condensed octahedral units, sharing a common edge, coincident with the ideal three-fold axis. The carbonyl stereochemistry however is different in (1) and (2), as well as the pattern of metal–metal bonds. Complexes (1) and (2) have identical i.r. spectra in solution and variable-temperature 13C n.m.r. spectra show that the ligands are completely fluxional, even at –90 °C.

Multinuclear n.m.r. studies (1H, 1H-{103Rh}, l3C, 13C-{103Rh}, and 103Rh) show that protonation of [Rh6(CO)15]2– and [Rh6(CO)15C]2– at low temperatures gives [Rh6H(CO)15]– and [Rh6H(CO)15C]– which contain terminal and triangular face-bridging hydrides respectively;warming these solutions to room temperature results in loss of hydrogen and formation of [Rh12(CO)30]2– and [Rh12(CO)24(C)2]2– respectively.

The synthesis and spectroscopic properties of some complexes of the type trans-[RhCl2(N–N′)2]+(N–N′=N-methyl-,NN′-dimethyl-,NN-dimethyl,NNN′-trimethyl-, and NNN′N′-tetramethyl-ethane-1,2-diamine, men, sdmen, udmen, trimen, and tetmen, respectively) are described and the previously reported route to trans-[RhCl2(udmen)2]+ is shown to give a cis-isomer. The chemical and polarographic-reduction behavious of the complexes is reported together with a kinetic study of chloride–bromide exchange in trans-[RhCl2(N–N′)2]+(N–N′= men, udmen, trimen, or tetmen). The activation parameters for the reaction of trans-[RhCl2(tetmen)2]+ with bromide ion have been determined and are discussed in relation to literature data for the analogous reactions of trans-[RhCl2(en)2]+and trans-[RhCl2(NH3)4]+.

The reductive carbonylations of mixtures of Na2PtC16 and RhC13.xH20 (at room temperature and 1 atm CO) are reported. From the reaction mixtures [PtRh5(CO)15]- and [PtRh4(CO)14]2- have been isolated; the latter is in equilibrium, through the release and absorption of CO, with [PtRh4(CO)12]2-. Solution structures and fluxional behavior of all these anions have been established by multinuclear (13C, 13C-{103Rh}, 103Rh, 195Pt) variable-temperature NMR measurements.

Isotopic labelling of the interstitial atom in [M6(CO)15C]2- and [M6(CO)15N]- enabled the metal-interstitial atom frequencies to be assigned and the associated force constants, f(ax) and f(eq), are found to be very similar for the M6-C and M6-N groups, with the values for M = Rh being significantly smaller than when M = Co.

The synthesis and the structure of the novel tri-anion, [Fe 3 Rh 3 (CO) 17 ] 3− , is reported: the metal framework of this 88 valence electron bimetallic cluster is unusual, and consists of an Fe 2 Rh 3 trigonal bipyramid with iron and rhodium atoms in apical sites and a dangling Fe atom attached to the apical Rh.

Bromination of 2-(alkenyl)pyridine (L) complexes, trans-[PtBr2(PEt3)L], gives PtIV–C σ-bonded complexes and the mechanism of these and related reactions is discussed.

Carbonylations reductrices des melanges de Na 2 PtCl 6 et RhCl 3 •xH 2 O. On a pu ainsi isoler [PtRh 5 (CO) 15 ] − et [PtRh 4 (CO) 14 ] 2− . Structure en solution

The [Rh5Pt(CO)11(µ3-CO)4]– anion, which has been prepared by two independent routes, is shown to be structurally related to [Rh6(CO)12(µ3-CO)4][one Rh(CO)2 group is replaced by a Pt(CO) group] both in the solid state (X-ray) and in solution (n.m.r.); evidence is also presented for a further reduced mixed anion [Rh2Pt-(CO)x]n–.

The first example of carbonyl clusters containing fully interstitial germanium and tin atoms have been isolated from the reaction of their chlorides with [Ni6(CO)12]2–; the structures of the icosahedral [Ni12Ge(CO)22]2– and [Ni12Sn(CO)22]2– and the pentagonal antiprismatic [Ni10Ge(CO)20]2– have been established from X-ray diffraction studies.

The 13C n.m.r. spectrum of [Rh12(CO)30]2– is shown to be fully consistent with X-ray structural data and provides the first example of a triply bridging carbonyl resonance.

1 H, 1H–{103Rh} INDOR, and 13C n.m.r. spectroscopy has been used to show that the hydrogens in [Rh13(CO24)H5 –n]n–(n= 2 or 3) migrate rapidly around the inside of the hexagonal close-packed cluster; 13C n.m.r. spectroscopy also shows that at room temperature all the edge-bridging carbonyl groups, except for the 3 carbonyl groups which bridge the rhodium atoms in the hexagonal plane, undergo exchange with the 12 terminal carbonyl groups on the outside of the cluster.

The syntheses and interconversions of mixed iron–rhodium carbonyl clusters are described; a combination of X-ray analysis and multinuclear n.m.r. measurements allowed the structural characterisation of [FeRh4(CO)15]2–, [FeRh5(CO)16]–, and [Fe2Rh4(CO)16]2–, which can all be obtained from the unstable cluster, [Fe2Rh(CO)x]–(x= 10 or 11).

The anion [Co6(CO)16P]– has been obtained by reaction of PCl3 with Na[Co(CO)4]; the six metal atoms form four triangles linked in a chain surrounding a ‘semi-interstitial’ phosphide atom.

The metal–metal stretching region of the i.r. and Raman spectra of [Rh4(CO)12] is reported and analysed. The hitherto unpublished solution and 13CO-enriched spectra suggest that the metal–metal region should be reassigned, and these results are compared with those for [Ir4(CO)12].

Carbon-13 n.m.r. measurements on rhodium carbonyl clusters in solutions under high pressures of gaseous CO/H2 are reported. Pressurization of solutions of [Rh12(CO)30]2– with CO (5 bar) shows that [Rh5(CO)15]– is formed quantitatively and that, below 298 K, further fragmentation does not occur on pressurization up to 1 kbar with CO/H2. Variable-temperature measurements on [Rh5(CO)15]– show that the rate of inter-exchange of carbonyls with carbon monoxide at high pressure is slow on the n.m.r. time-scale and that, at room temperature, all the carbonyls, except the three bridging the Rh3 equatorial plane, undergo intra-exchange. At high 13C enrichments, the resonance due to the equatorial bridging carbonyls becomes complex due to an increasing abundance of isotopomers, Rh3(µ-12COeq.)3 –x(µ-13COeq.)x(x= 0–3), with larger values of x for which 2J(Ceq.–Ceq)= 20 Hz. Despite claims to the contrary, the apex-connected, double-octahedral metallic skeleton in [Rh12(CO)30]2– remains intact up to 323 K under a nitrogen atmosphere. The high-resolution n.m.r. probe for measurements on solutions under 1 kbar pressures of CO and H2 gases is described.

A combination of variable-temperature, multinuclear n.m.r. studies (1H, 13C, 103Rh, 1H-{103Rh}, and 13C-{103Rh}) has allowed the ligand (CO/H) migrations in [Rh13(CO)24Hn](5 –n)–(n= 1–4) and [Rh14(CO)25HX](4 –x)–(x= 0 or 1) to be established. In both types of compound, interstitial H migration is found at room temperature with complete randomisation of carbonyls in the Rh14 clusters and partial migration of carbonyls in the Rh13 clusters; in neither case is there evidence for rearrangement of the metal polyhedron. At low temperatures (–90 °C), H migration still occurs in [Rh14(CO)25H]3– but not in [Rh13(CO)24H3]2– and [Rh13(CO)24H2]3– which have the same structural features as found in the solid state with the hydride ligands occupying pseudooctahedral holes in the metal skeleton. All the values of δ(103Rh) for the interstitial rhodium atoms are at significantly higher frequency than the values for the surface rhodium resonances and shift significantly to lower frequency with increasing interstitial hydride content.

Reactions of 2-(alkenyl)pyridines with Group 6A hexacarbonyls and [M(CO)4(nbd)](M = Cr, Mo, or W; nbd = norbornadiene) are described. Isomerisation of the alkenyl side chain occurs with 2-(CR1MeCR2)-, 2-(CH2CR1CH2CH2)- and 2-(CH2CHCH2CH2CH2)-C5H4N (R1, R2= H or Me) to give complexes of the type [M(CO)4L][L = 2-(prop-2′-enyl)- or 2-(substituted prop-2′-enyl)-pyridine] which have, in some cases, also been prepared directly from L; L is always bidentate. The mechanism of isomerisation is discussed. Spectroscopic studies provide no evidence for conformational isomerism involving the plane of the co-ordinated olefin. Related reactions with Ph2P[CH2]2CHCH2 and Ph2P[CH2]3CHCH2 give [Mo(CO)4(Ph2PCH2CH2CHCH2)] and [Mo(CO)4(Ph2PCH2CH2CH2CHCH2)2] respectively.