Structural rearrangements induced by acid–base reactions in metal carbonyl clusters: the case of [H_3−nCo₁₅Pd₉C₃(CO)₃₈]ⁿ⁻(n = 0–3)

Abstract

The new bimetallic [HCo15Pd9C3(CO)38](2-) tri-carbide carbonyl cluster has been obtained from the reaction of [H2Co20Pd16C4(CO)48](4-) with an excess of acid in CH2Cl2 solution. The mono-hydride di-anion can be reversibly protonated and deprotonated by means of acid-base reactions leading to closely related [H(3-n)Co15Pd9C3(CO)38](n-) (n = 0-3) clusters. The crystal structures of the three anionic and the neutral clusters have been determined as their H3Co15Pd9C3(CO)38·2thf, [NEt4][H2Co15Pd9C3(CO)38]·0.5C6H14, [NMe3(CH2Ph)]2[HCo15Pd9C3(CO)38]·C6H14 and [NEt4]3[Co15Pd9C3(CO)38]·thf salts. They are composed of a Pd9(μ3-CO)2 core stabilised by three Co5C(CO)12 organometallic fragments. The poly-hydride nature of these clusters has been indirectly inferred via chemical, electrochemical and magnetic measurements. Besides, cyclic voltammetry shows that the [H(3-n)Co15Pd9C3(CO)38](n-) (n = 1-3) anions are multivalent, since they undergo two or three reversible oxidations. SQUID measurements of [HCo15Pd9C3(CO)38](2-) indicate that this even electron cluster is paramagnetic with two unpaired electrons, giving further support to its hydride nature. Finally, structural studies show that the Pd9 core of [H(3-n)Co15Pd9C3(CO)38](n-) (n = 0,1) is a tri-capped octahedron, which becomes a tri-capped trigonal prism in the more charged [H(3-n)Co15Pd9C3(CO)38](n-) (n = 2,3) anions. Such a significant structural rearrangement of the metal core of a large carbonyl cluster upon protonation-deprotonation reactions is unprecedented in cluster chemistry, and suggests that interstitial hydrides may have relevant stereochemical effects even in large carbonyl clusters.

Cluster Core Isomerism Induced by Crystal Packing Effects in the [HCo15Pd9C3(CO)38]2– Molecular Nanocluster

“…The synthetic protocol adopted in this work is very similar to that adopted and described in our previous paper. 30 The major variation is represented by the exchange of the cation prior to the synthesis of [HCo 15 Pd 9 C 3 (CO) 38 ] 2– (Scheme 2). Thus, [NMe 3 (CH 2 Ph)] 4 [H 2 Co 20 Pd 16 C 4 (CO) 48 ] was synthesized by reacting [NMe 3 (CH 2 Ph)] 2 [Co 6 C(CO) 15 ] and Pd(Et 2 S)Cl 2 in thf according to the literature procedure.…”

“…This, in turn, was converted into H 3 Co 15 Pd 9 C 3 (CO) 38 during crystallization in the presence of an excess of HBF 4 ·Et 2 O. 30 In the attempt to obtain new crystal salts of [CAT][H 2 Co 15 Pd 9 C 3 (CO) 38 ] and H 3 Co 15 Pd 9 C 3 (CO) 38 , the whole procedure was repeated several times by further increasing the amount of the acid employed. Even if this was unsuccessful, when a very large excess of HBF 4 ·Et 2 O was employed, a few crystals of the [NMe 3 (CH 2 Ph)][Co 13 Pd 3 C 3 (CO) 29 ]·CH 2 Cl 2 salt were obtained.…”

“…Moreover, some crystallographic disorder has been found in the metal core of the former molecule, which can be better described as 91% TP-Pd 9 and 9% Oh-Pd 9 .The Pd 9 core of [NMe 3 (CH 2 Ph)] 2 [HCo 15 Pd 9 C 3 (CO) 38 ]·2CH 2 Cl 2 ( 2 ) adopts a TP-Pd 9 structure, even if some crystallographic disorder (<9%) is present.The Pd 9 core of [NEt 3 (CH 2 Ph)] 2 [HCo 15 Pd 9 C 3 (CO) 38 ]·CH 2 Cl 2 ( 3 ) is again TP-Pd 9 (94%), with a minor contribution (6%) from an Oh-Pd 9 structure.[MePPh 3 ] 2 [HCo 15 Pd 9 C 3 (CO) 38 ]·2.5CH 2 Cl 2 ( 5 ) displays a TP-Pd 9 core.[MePPh 3 ] 2 [HCo 15 Pd 9 C 3 (CO) 38 ] ( 7 ) displays a perfectly ordered Oh-Pd 9 core.The previously reported [NMe 3 (CH 2 Ph)] 2 [HCo 15 Pd 9 C 3 (CO) 38 ]·C 6 H 14 salt displayed a TP-Pd 9 core. 30 …”

“…To address this question, we have re-examined the structures of the [H 3– n Co 15 Pd 9 C 3 (CO) 38 ] n − ( n = 0–3) molecular nanoclusters. 30 These species may be reversibly interconverted by acid–base reactions, as summarized in Scheme 1. Their molecular structures were originally determined as their H 3 Co 15 Pd 9 C 3 (CO) 38 ·2thf, [NEt 4 ][H 2 Co 15 Pd 9 C 3 (CO) 38 ]·0.5C 6 H 14 , [NMe 3 (CH 2 Ph)] 2 [HCo 15 Pd 9 C 3 (CO) 38 ]·C 6 H 14 , and [NEt 4 ] 3 [Co 15 Pd 9 C 3 (CO) 38 ]·thf solids and salts.…”

“…Pd 9 cores of (a) H 3 Co 15 Pd 9 C 3 (CO) 38 , (b) [H 2 Co 15 Pd 9 C 3 (CO) 38 ] − , (c) [HCo 15 Pd 9 C 3 (CO) 38 ] 2– , and (d) [Co 15 Pd 9 C 3 (CO) 38 ] 3– as originally determined. 30 …”