Iacopo Ciabatti

Bimetallic Fe–Au Carbonyl Clusters Derived from Collman’s Reagent: Synthesis, Structure and DFT Analysis of Fe(CO)4(AuNHC)2 and [Au3Fe2(CO)8(NHC)2]−

The reaction of the Collman’s reagent Na2Fe(CO)4 with two equivalents of Au(NHC)Cl (NHCxa0=xa0IMes, IPr, IBu) in thf results in the bimetallic Fe(CO)4(AuNHC)2 (NHCxa0=xa0IMes, 2; IPr, 3; IBu, 4; IMesxa0=xa0C3N2H2(C6H2Me3)2; IPrxa0=xa0C3N2H2(C6H3iPr2)2; IBuxa0=xa0C3N2H2(CMe3)2) clusters in good yields. Heating 2 in dmf at 100xa0°C results in the higher nuclearity cluster [Au3Fe2(CO)8(IMes)2]− (5). 2–5 have been fully characterized via IR, 1H and 13C NMR spectroscopies and their structures determined by means of single crystal X-ray crystallography. Gas-phase DFT calculations were carried out on 2–5 and the model compound cis-Fe(CO)4(AuIDM)2 (6) (IDMxa0=xa0C3N2H2Me2), in order to better understand the metal–metal and metal–ligand interactions in these compounds without the influence of packing forces.

Heteroleptic Chini-Type Platinum Clusters: Synthesis and Characterization of Bis-Phospine Derivatives of [Pt3n(CO)6n]2– (n = 2–4)

The reactions of [Pt3n(CO)6n]2- (n = 2-4) homoleptic Chini-type clusters with stoichiometric amounts of Ph2PCH2CH2PPh2 (dppe) result in the heteroleptic Chini-type clusters [Pt6(CO)10(dppe)]2-, [Pt9(CO)16(dppe)]2-, and [Pt12(CO)20(dppe)2]2-. Their formation is accompanied by slight amounts of neutral species such as Pt4(CO)4(dppe)2, Pt6(CO)6(dppe)3, and Pt(dppe)2. A similar behavior was observed with the chiral ligand R-Ph2PCH(Me)CH2PPh2 (R-dppp), and two isomers of [Pt9(CO)16(R-dppp)]2- were identified. All the new species were spectroscopically characterized by means of IR and 31P NMR, and their structures were determined by single-crystal X-ray diffraction. The results obtained are compared to those previously reported for monodentate phosphines, that is, PPh3, as well as more rigid bidentate ligands, that is, CH2═C(PPh2)2 (P^P), CH2(PPh2)2 (dppm), and o-C6H4(PPh2)2 (dppb). From a structural point of view, functionalization of anionic platinum Chini clusters preserves their triangular Pt3 units, whereas the overall trigonal prismatic structures present in the homoleptic clusters are readily deformed and transformed upon functionalization. Such transformations may be just local deformations, as found in [Pt9(CO)16(dppe)]2-, [Pt9(CO)16(R-dppp)]2-, [Pt12(CO)22(PPh3)2]2-, and [Pt9(CO)16(PPh3)2]2-; an inversion of the cage from trigonal prismatic to octahedral, as observed in [Pt6(CO)10(dppe)]2- and [Pt6(CO)10(PPh3)2]2-; the reciprocal rotation of two trigonal prismatic units with the loss of a Pt-Pt contact as found in [Pt12(CO)20(dppe)2]2-.

Reactions of Platinum Carbonyl Chini Clusters with Ag(NHC)Cl Complexes: Formation of Acid–Base Lewis Adducts and Heteroleptic Clusters

The reactions of anionic platinum carbonyl Chini clusters [Pt3n(CO)6n]2- [n = 2 (1), 3 (2), 4 (3)] with Ag(IPr)Cl [IPr = C3N2H2(C6H3iPr2)2] afford the neutral acid-base Lewis adducts [Pt9(CO)18(AgIPr)2] (4) and [Pt6(CO)12(AgIPr)2] (5). These are thermally transformed into the homometallic heteroleptic neutral cluster [Pt3(CO)4(IPr)2] (6). Alternatively, 6 can be obtained from the reactions of 1-3 with an excess of the free IPr carbene ligand. The formation of 6 is sometimes accompanied by trace amounts of [Pt4(CO)4(IPr)3] (7). The reaction of 6 with free IPr affords the closely related [Pt3(CO)3(IPr)3] (8) heteroleptic cluster by substitution of the unique terminal CO ligand with a third IPr ligand. The reactions of 1-3 with Ag(IMes)Cl [IMes = C3N2H2(C6H2Me3)2] proceed differently from those involving Ag(IPr)Cl. Indeed, the only product isolated after workup is the bimetallic tetranuclear cluster [Pt3(CO)3(IMes)3(AgCl)] (9). 9 slowly reacts under a CO atmosphere, resulting in the pentanuclear [Pt5(CO)7(IMes)3] (10) complex. All of the new clusters 4-10 have been spectroscopically characterized and their molecular structures determined by X-ray crystallography. 4 and 5 retain the original trigonal-prismatic structures of the parent anionic Chini clusters, which are capped by two [Ag(IPr)]+ moieties. Conversely, 6-9 are based on a Pt3 triangular core decorated by CO and N-heterocyclic carbene ligands as well as Pt(CO) (in the case of 7) and AgCl (9) moieties. 10 displays an edge-bridged tetrahedral geometry.

Interstitial Bismuth Atoms in Icosahedral Rhodium Cages: Syntheses, Characterizations, and Molecular Structures of the [Bi@Rh12(CO)27]3–, [(Bi@Rh12(CO)26)2Bi]5–, [Bi@Rh14(CO)27Bi2]3–, and [Bi@Rh17(CO)33Bi2]4– Carbonyl Clusters

The reaction of [Rh7(CO)16]3- with BiCl3 under N2 and at room temperature results in the formation of the new heterometallic [Bi@Rh12(CO)27]3- cluster in high yields. Further controlled addition of BiCl3 leads first to the formation of the dimeric [(Bi@Rh12(CO)26)2Bi]5- and the closo-[Bi@Rh14(CO)27Bi2]3- species in low yields, and finally, to the [Bi@Rh17(CO)33Bi2]4- cluster. All clusters were spectroscopically characterized by IR and electrospray ionization mass spectrometry, and their molecular structures were fully determined by X-ray diffraction studies. Notably, they represent the first examples of Bi atoms interstitially lodged in metallic cages that, in this specific case, are all based on an icosahedral geometry. Moreover, [Bi@Rh14(CO)27Bi2]3- forms an exceptional network of infinite zigzag chains in the solid state, thanks to intermolecular Bi-Bi distances.

Synthesis of [Pt12(CO)20(dppm)2]2– and [Pt18(CO)30(dppm)3]2– Heteroleptic Chini-type Platinum Clusters by the Oxidative Oligomerization of [Pt6(CO)12(dppm)]2–

The reactions of [Pt6(CO)12]2- with CH(PPh2)2 (dppm), CH2═C(PPh2)2 (P^P), and Fe(C5H4PPh2)2 (dppf) proceed via nonredox substitution and result in the heteroleptic Chini-type clusters [Pt6(CO)10(dppm)]2-, [Pt6(CO)10(P^P)]2-, and [Pt6(CO)10(dppf)]2-, respectively. Conversely, the reactions of [Pt6(CO)12]2- with Ph2P(CH2)4PPh2 (dppb) and Ph2PC≡CPPh2 (dppa) can be described as redox fragmentation that afford the neutral complexes Pt(dppb)2, Pt2(CO)2(dppa)3, and Pt8(CO)6(PPh2)2(C≡CPPh2)2(dppa)2. The oxidation of [Pt6(CO)10(dppm)]2- results in its oligomerization to yield the larger heteroleptic Chini-type clusters [Pt12(CO)20(dppm)2]2-, [Pt18(CO)30(dppm)3]2-, and [Pt24(CO)40(dppm)4]2- (for the latter there is only IR spectroscopic evidence). All the clusters were characterized by means of IR and 31P NMR spectroscopies and electrospray ionization mass spectrometry. Moreover, the crystal structures of [NEt4]2[Pt6(CO)10(dppm)]·CH3CN, [NEt4]2[Pt12(CO)20(dppm)2]·2CH3CN·2dmf, [NEt4]2[Pt12(CO)20(dppm)2]·4dmf, [NEt4]2[Pt6(CO)10(dppf)]·2CH3CN, Pt2(CO)2(dppa)3·0.5CH3CN, Pt8(CO)6(PPh2)2(C≡CPPh2)2(dppa)2·2thf, and Pt(dppb)2 were determined by single-crystal diffraction (dmf = dimethylformamide; thf = tetrahydrofuran).

Molecular Nickel Phosphide Carbonyl Nanoclusters: Synthesis, Structure, and Electrochemistry of [Ni11P(CO)18]3– and [H6–nNi31P4(CO)39]n− (n = 4 and 5)

The reaction of [NEt4]2[Ni6(CO)12] in thf with 0.5 equiv of PCl3 affords the monophosphide [Ni11P(CO)18]3- that in turn further reacts with PCl3 resulting in the tetra-phosphide carbonyl cluster [HNi31P4(CO)39]5-. Alternatively, the latter can be obtained from the reaction of [NEt4]2[Ni6(CO)12] in thf with 0.8-0.9 equiv of PCl3. The [HNi31P4(CO)39]5- penta-anion is reversibly protonated by strong acids leading to the [H2Ni31P4(CO)39]4- tetra-anion, whereas deprotonation affords the [Ni31P4(CO)39]6- hexa-anion. The latter is reduced with Na/naphthalene yielding the [Ni31P4(CO)39]7- hepta-anion. In order to shed light on the polyhydride nature and redox behavior of these clusters, electrochemical and spectroelectrochemical studies were carried out on [Ni11P(CO)18]3-, [HNi31P4(CO)39]5-, and [H2Ni31P4(CO)39]4-. The reversible formation of the stable [Ni11P(CO)18]4- tetra-anion is demonstrated through the spectroelectrochemical investigation of [Ni11P(CO)18]3-. The redox changes of [HNi31P4(CO)39]5- show features of chemical reversibility and the vibrational spectra in the νCO region of the nine redox states of the cluster [HNi31P4(CO)39]n- (n = 3-11) are reported. The spectroelectrochemical investigation of [H2Ni31P4(CO)39]4- revealed the presence of three chemically reversible reduction processes, and the IR spectra of [H2Ni31P4(CO)39]n- (n = 4-7) have been recorded. The different spectroelectrochemical behavior of [HNi31P4(CO)39]5- and [H2Ni31P4(CO)39]4- support their formulations as polyhydrides. Unfortunately, all the attempts to directly confirm their poly hydrido nature by 1H NMR spectroscopy failed, as previously found for related large metal carbonyl clusters. Thus, the presence and number of hydride ligands have been based on the observed protonation/deprotonation reactions and the spectroelectrochemical experiments. The molecular structures of the new clusters have been determined by single-crystal X-ray analysis. These represent the first examples of structurally characterized molecular nickel carbonyl nanoclusters containing interstitial phosphide atoms.

Capping [H8−nNi42C8(CO)44]n− (n = 6, 7, 8) Octa-carbide Carbonyl Nanoclusters with [Ni(CO)] and [CuCl] Fragments

The reactions of [Ni16(C2)2(CO)23]4− and [Ni38C6(CO)42]6− with CuCl afforded mixtures of the previously reported [HNi42C8(CO)44(CuCl)]7− bimetallic octa-carbide cluster and the new [HNi43C8(CO)45]7− and [HNi44C8(CO)46]7− homo-metallic octa-carbides. The three species have very similar properties resulting always in co-crystals such as [NMe4]7[HNi42+2xC8(CO)44+2x(CuCl)1−x]·6.5MeCN (xxa0=xa00.14) (86% [HNi42C8(CO)44(CuCl)]7−, 14%[HNi43C8(CO)45]7−/[HNi44C8(CO)46]7−) and [NMe4]7[HNi42+2xC8(CO)44+2x(CuCl)1−x]·5.5MeCN (xxa0=xa00.30) (70% [HNi42C8(CO)44(CuCl)]7−, 30% [HNi43C8(CO)45]7−/[HNi44C8(CO)46]7−). The new homo-metallic octa-carbides can be obtained free from the Ni–Cu octa-carbido cluster by reacting [Ni10(C2)(CO)16]2− in thf with a stoichiometric amount of CuCl, and crystals of [NMe4]6[H2Ni43+xC8(CO)45+x]·6MeCN (xxa0=xa00.72), which contain [H2Ni44C8(CO)46]6− (72%) and [H2Ni43C8(CO)45]6− (28%), have been obtained. Despite the different charges and compositions, these anions display almost identical structures, which are also closely related to those previously reported for the bimetallic Ni–Cd octa-carbido clusters [Ni42+xC8(CO)44+x(CdCl)]7− and [HNi42+xC8(CO)44+x(CdBr)]6−. Indeed, all these clusters are based on the same Ni42C8 cage decorated by miscellaneous [CdX]+ (Xxa0=xa0Cl, Br), [CuCl] and [Ni(CO)] fragments.