Molybdenum and tungsten structural differences are dependent on nd(Z)(2)/(n+1)s mixing: Comparisons of (silox)(3)MX/R (M = Mo, W; silox = (Bu3SiO)-Bu-t)

David S. Kuiper, Richard E. Douthwaite, Ana-Rita Mayol, Peter T. Wolczanski, Emil B. Lobkovsky, Thomas R. Cundari, Oanh P. Lam, Karsten Meyer

Research output: Contribution to journalArticlepeer-review

Abstract

Treatment of trans-(Et2O)(2)MoCl4 with 2 or 3 equiv of Na(silox) (i.e., (NaOSiBu3)-Bu-t) afforded (Silox)(3)MoCl2 (1-Mo) or (silox)(3)MoCl (2-Mo). Purification of 2-Mo was accomplished via addition of PMe3 to precipitate (Silox)(3)CIMoPMe3 (2-MoPMe3), followed by thermolysis to remove phosphine. Use of MoCl3(THF)(3) with various amounts of Na(silox) produced (Silox)(2)ClMoMoCl(Silox)(2) (3-Mo). Alkylation of 2-Mo with MeMgBr or EtMgBr afforded (Silox)(3)MoR (R = Me, 2-MoMe; Et, 2-MoEt). 2-MoEt was also synthesized from C2H4 and (Silox)(3)MoH, which was prepared from 2-Mo and NaBEt3H. Thermolysis of WCl6 with (HOSiBu3)-Bu-t afforded (Silox)(2)WCl4 (4-W), and sequential treatment of 4-W with Na/Hg and Na(silox) provided (Silox)(3)WCl2 (1-W, tbp, X-ray), which was alternatively prepared from trans-(Et2S)(2) WCl4 and 3 equiv of Tl(silox). Na/Hg reduction of 1-W generated (silox)(3)WCl (2-W). Alkylation of 2-W with MeMgBr produced (Silox)(3)WMe (2-WMe), which dehydrogenated to (Silox)(3)WCH (6-W) with Delta H-double dagger = 14.9(9) kcal/ mol and Delta S-double dagger = -26(2) eu. Magnetism and structural studies revealed that 2-Mo and 2-MoEt have triplet ground states (GS) and distorted trigonal monopyramid (tmp) and tmp structures, respectively. In contrast, 2-W and 2-WMe possess squashed-T-d (distorted square planar) structures, and the former has a singlet GS. Quantum mechanics/ molecular mechanics studies of the S = 0 and S = 1 states for full models of 2-Mo, 2-MoEt, 2-W and 2-WMe corroborate the experimental findings and are consistent with the greater nd(z)(2)/(n + 1)s mixing in the third-row transition-metal species being the dominant feature in determining the structural disparity between molybdenum and tungsten.

Original languageEnglish
Pages (from-to)7139-7153
Number of pages15
JournalInorganic Chemistry
Volume47
Issue number16
DOIs
Publication statusPublished - 18 Aug 2008

Keywords

  • FORBIDDEN CHEMICAL-REACTIONS
  • TRANSITION-METAL-COMPLEXES
  • OPEN-SHELL ORGANOMETALLICS
  • ELECTRONIC-STRUCTURE
  • BIS(DITHIOLENE) COMPLEXES
  • REACTION SYSTEMS
  • ALKYL COMPLEXES
  • BOND ACTIVATION
  • ATOM-TRANSFER
  • C-H

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