Molar-Ratio-Dependent Coordination Assembly of Organoiridium(III)-Octatungstate Complexes in Aqueous Solution

Abstract

We scrutinized the speciation of Cp*Ir-containing tungsten oxide clusters (Cp* is pentamethylcyclopentadienyl anion) in aqueous mixtures of [(Cp*IrCl)2(μ-Cl)2] and Na2WO4 in varying molar ratios. 1H nuclear magnetic resonance (NMR) spectroscopy revealed the formation of three distinct Cp*Ir–polyoxotungstate species in the reaction solution, and they were isolated as Na4[(Cp*Ir)2(μ-OH)3]2[(Cp*Ir)2H2W8O30] (1), [(Cp*Ir)2(μ-OH)3]2[(Cp*Ir)2{Cp*Ir(OH2)}2H2W8O30] (2), and [(Cp*Ir)2{Cp*Ir(OH2)}2{Cp*Ir(OH2)2}2H2W8O30](NO3)2 (3) from the mixtures in which iridium concentration is less than, equal to, and more than the tungsten concentration, respectively. These results show the octatungstate [H2W8O30]10– anion is the major polyoxotungstate species in the presence of {Cp*Ir}2+ cations, and it has high nucleophilicity enough to bind up to six {Cp*Ir}2+ cations on its surfaces producing a cationic Cp*Ir–octatungstate complex. The octatungstate anion was also generated from the reaction of [(Cp*IrCl)2(μ-Cl)2] and methylammonium paratungstate-B, (CH3NH3)10[H2W12O42], and was isolated as a methylamine-coordinated complex (CH3NH3)2[(Cp*Ir)2{Cp*Ir(NH2CH3)}2H2W8O30] (4), indicating {Cp*Ir}2+ cations function as a structure-directing agent that converts tungsten species into octatungstate anions in aqueous solution. In addition, the coordination environment of {Cp*Ir}2+ can be further modified by coordination with pyridine forming [{Cp*Ir(NC5H5)}2(μ-OH)2][(Cp*Ir)2{Cp*Ir(NC5H5)}2H2W8O30] (5).

Solid/Gas In Crystallo Reactivity of an Ir(I) Methylidene Complex

“…The corresponding SSNMR spectra are essentially the same. These NMR and metrical data are consistent with previously reported Ir-NH 2 Me complexes. , …”

Reactivity of Organoiridium Tungsten Oxide Clusters with Transition Metal Aquo Cations

“…As shown in Figure a, 1 consists of a tetra-(Cp*Ir)-grafted octatungstate [{Cp*Ir­(OH 2 )} 2 (Cp*Ir) 2 H 2 W 8 O 30 ] 2– (Ir 4 W 8 , see Scheme ) anionic core with two additional {Ag­(OH 2 ) 2 } + fragments, and hence, 1 is a charge-neutral complex. The Ir 4 W 8 anion has been reported by Niu et al and recently by us and is made up of cubane-type {Cp*IrW 3 O 12 (OH)} 5– , bridging cis -{WO 2 } 2+ , and dangling {Cp*Ir­(OH 2 )} 2+ fragments; the {Cp*IrW 3 O 12 (OH)} 5– fragment is also the building units in 2-Co , 2-Ni , 3-Cr , 3-Fe , and 3-In , see below.…”

“…Recently, we reported that the reaction of [(Cp*IrCl) 2 (μ-Cl) 2 ] and Na 2 WO 4 in aqueous solutions produces a highly nucleophilic octatungstate [{W 3 O 12 (OH)} 2 (WO 2 ) 2 ] 10– anion, which is capped by multiple {Cp*Ir} 2+ fragments (Scheme ). Our question was whether the {Cp*Ir} 2+ cations are substitutable to Werner-type transition-metal aquo cations. Herein, we demonstrate that the addition of Ag + , Co 2+ , Ni 2+ , and M 3+ (M = Cr, Fe, or In) cations into the aqueous solution of Cp*Ir-octatungstate clusters produces [{Ag­(OH 2 ) 2 } 2 ­{Cp*Ir­(OH 2 )} 2 ­{Cp*IrW 3 O 12 (OH)} 2 ­(WO 2 ) 2 ] ( 1 ), Co 1.5 K 0.8 Na 0.2 ­[{ trans -Co­(OH 2 ) 2 }­{Cp*IrW 3 O 12 (OH)} 2 ­(WO 2 ) 1.3 ­{ cis -Co­(OH 2 ) 2 } 0.7 ] ( 2-Co ), Ni 0.2 K 1.4 Na 0.2 ­[{Ni­(OH 2 ) 4 } 2 ­{Cp*IrW 3 O 12 (OH)} 2 ­(WO 2 ) 1.1 ­{ cis -Ni­(OH 2 ) 2 } 0.9 ] ( 2-Ni ), and [{M­(OH 2 ) 4 } 2 ­{Cp*IrW 3 O 12 (OH)} 2 ­{ cis -M­(OH 2 ) 2 } 2 ]­(NO 3 ) 2 (M = Cr, 3-Cr ; Fe, 3-Fe ; or In 3-In ), respectively (Scheme ).…”