Molecular Nickel Phosphide Carbonyl Nanoclusters: Synthesis, Structure, and Electrochemistry of [Ni₁₁P(CO)₁₈]^3–and [H_6–nNi₃₁P₄(CO)₃₉]ⁿ⁻(n= 4 and 5)

Abstract

The reaction of [NEt][Ni(CO)] in thf with 0.5 equiv of PCl affords the monophosphide [NiP(CO)] that in turn further reacts with PCl resulting in the tetra-phosphide carbonyl cluster [HNiP(CO)]. Alternatively, the latter can be obtained from the reaction of [NEt][Ni(CO)] in thf with 0.8-0.9 equiv of PCl. The [HNiP(CO)] penta-anion is reversibly protonated by strong acids leading to the [HNiP(CO)] tetra-anion, whereas deprotonation affords the [NiP(CO)] hexa-anion. The latter is reduced with Na/naphthalene yielding the [NiP(CO)] 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 [NiP(CO)], [HNiP(CO)], and [HNiP(CO)]. The reversible formation of the stable [NiP(CO)] tetra-anion is demonstrated through the spectroelectrochemical investigation of [NiP(CO)]. The redox changes of [HNiP(CO)] show features of chemical reversibility and the vibrational spectra in the ν region of the nine redox states of the cluster [HNiP(CO)] (n = 3-11) are reported. The spectroelectrochemical investigation of [HNiP(CO)] revealed the presence of three chemically reversible reduction processes, and the IR spectra of [HNiP(CO)] (n = 4-7) have been recorded. The different spectroelectrochemical behavior of [HNiP(CO)] and [HNiP(CO)] support their formulations as polyhydrides. Unfortunately, all the attempts to directly confirm their poly hydrido nature by H 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.

Structural Diversity in Molecular Nickel Phosphide Carbonyl Nanoclusters

“…The synthesis of Ni–P–CO clusters is very sensitive to experimental conditions (Scheme ), that is, the stoichiometric ratio, counterion, solvent, and P source. Thus, by reacting [Ni 6 (CO) 12 ] 2– as a [NEt 4 ] + salt with PCl 3 in thf, [Ni 11 P­(CO) 18 ] 3– and, then, [HNi 31 P 4 (CO) 39 ] 5– were formed in sequence, as previously reported . Conversely, carrying out a similar reaction in CH 2 Cl 2 with [NBu 4 ] + as a counterion, [Ni 14 P 2 (CO) 22 ] 2– was obtained.…”

“…Only two molecular Ni–P carbonyl nanoclusters have been characterized so far, that is, [Ni 11 P­(CO) 18 ] 3– and [H 6– n Ni 31 P 4 (CO) 39 ] n − ( n = 4, 5) . The unique P atom of [Ni 11 P­(CO) 18 ] 3– is enclosed within a Ni 10 spheonocorona cage, whereas [H 6– n Ni 31 P 4 (CO) 39 ] n − ( n = 4, 5) contains two distorted Ni 9 P monocapped square antiprisms and two distorted Ni 10 P bicapped square antiprisms.…”

Functionalization, Modification, and Transformation of Platinum Chini Clusters

“…The reactions of metal carbonyl anions such as [Ni 6 (CO) 12 ] 2– and [Rh 7 (CO) 15 ] 3– with miscellaneous MX n salts (M = Pd, Pt, Au, Ga, Ge, Sn, Sb, Bi, etc. ), or related complexes, have been widely employed for the synthesis of bimetallic [M x M′ y (CO) z ] m – clusters via redox condensation , , , , . Analogous reactions involving [Pt 3 n (CO) 6 n ] 2– ( n = 2–6) Chini clusters usually follow different routes, as described in Section 2.3, resulting into (a) larger homoleptic Chini clusters (Section 2.1), (b) surface decorated Pt carbonyl clusters (this section) or (c) acid‐base Lewis adducts of Chini clusters (Section 2.3).…”

“…[H 2 Pt 26 (CO) 20 (CdBr) 12 ] 8– is actually a polyhydride which undergoes to a complex series of protonation/deprotonation reactions (Scheme ), as often observed for large anionic metal carbonyl clusters . The identification of hydrides within the metal cage of large nanoclusters and ultra‐small metal nanoparticles is a challenge which often defeats the actual spectroscopic and structural methods, that is NMR and single‐crystal X‐ray diffraction , , , . Neutron diffraction is the only technique which can directly locate hydride ligands in large molecular clusters, but it requires still rather big crystals.…”

“…Neutron diffraction is the only technique which can directly locate hydride ligands in large molecular clusters, but it requires still rather big crystals. Indirect methods have been, then, developed, for the identification of the hydride nature of such clusters and metal nanoparticles , , , . These include electrochemical and spectroelectrochemical methods in the case of high nuclearity metal carbonyl clusters,, , , , whereas solid state deuterium NMR has been employed in the case of Ru nanoparticles …”