Linear and Bent Nitric Oxide Ligand Binding in an Asymmetric Butterfly Complex: CoMoCo′

Abstract

Two synthetic approaches to install metallodithiolate ligands on molybdenum centers using the synthons [Mo 2 (CH 3 CN) 10 ] 4+ and (N 2 S 2 )Co(NO) [N 2 S 2 = N,N-bis(2-mercaptoethyl)-1,4-diazacycloheptane and NO = nitric oxide], or [Mo(NO) 2 (CH 3 CN) 4 ] 2+ (CH 3 CN = acetonitrile) and [(N 2 S 2 )Co] 2 lead to a bisnitrosylated, trimetallic dication, CoMoCo′. This unique asymmetric butterfly complex, with S = 1, has a bent NO within the small {Co(NO)} 8 wing (denoted as Co), reflecting Co III (NO − ), and is S-bridged to a linear {Mo(NO)} 6 diamagnetic unit. The latter is further S-bridged to a pentacoordinate (N 2 S 2 )Co III (CH 3 CN) donor in the larger wing and is the origin of the two unpaired electrons, denoted as Co′. The asymmetry in Mo−Co distances, 3.33 Å in the Co wing and 2.73 Å in the Co′ wing, indicated a Mo−Co′ bonding interaction. The transfer of NO from (N 2 S 2 )Co(NO) in the former path is needed to cleave the strong quadruple bond in [Mo≣Mo] 4+ , with the energetic cost compensated for via a one-electron bond between Mo and Co′, as indicated by natural bonding orbital analysis.

Sulfur Lone Pairs Control Topology in Heterotrimetallic Complexes: An Experimental and Theoretical Study

“…Previously, we determined CoMoCo′ , Figure , to have a triplet ground state originating from intermediate spin Co III on the Co′ . To gain insight into this triplet state, we investigated the magnetic moment temperature dependence, Figure c.…”

“…An application of these strategies toward derivatives of molybdenum, expected to be analogous to a class of [(bis-diphosphine) 2 M(NO)X] n+ molecules, 19 led to an unusual, asymmetric version of the basket structure of Figure 2. 20 Synthons include the [Mo 2 (MeCN) 10 ] 4+ source, which in our first studies in this area found that combination with (N 2 S 2 )Ni produced the Mo 2 Ni 4 paddlewheel structure (Figure 1d). 21 However, for (N 2 S 2 )Co(NO), as displayed in Figure 2, two cobalt ligands assemble about a single Mo atom.…”

“…90° produces a Mo–Co distance of 3.333 Å. The other indicates chemical noninnocence in that an NO/acetonitrile exchange has occurred, with NO transfer to molybdenum, generating a dinitrosylated trimetallic, dubbed CoMoCo ′, and whimsically described as an asymmetric butterfly, Figure . The denitrosylated Co, Co′ has MeCN in the apical position in the square pyramid.…”

“…In this "wing", the S−Co−S angle has opened to 108°, making possible a much shorter Mo−Co distance of 2.731 Å, defined by DFT computations as harboring a 1-electron bond. 20 The considerable bond/ electronic rearrangement in CoMoCo′ thus gains stability from the d 6 -Mo 0 (NO) + (a {Mo(NO)} 6 unit) 22 that adjusts electron density within a Mo 0 → Co III donation. According to DFT computations, this internal Mo−Co′ bond contributes to an isomeric stabilization of ca.…”

“…The other indicates chemical noninnocence in that an NO/acetonitrile exchange has occurred, with NO transfer to molybdenum, generating a dinitrosylated trimetallic, dubbed CoMoCo′, and whimsically described as an asymmetric butterfly, Figure 2. 20 The denitrosylated Co, Co′ has MeCN in the apical position in the square pyramid. In this "wing", the S−Co−S angle has opened to 108°, making possible a much shorter Mo−Co distance of 2.731 Å, defined by DFT computations as harboring a 1-electron bond.…”