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SUMMARY:Hydroformylation Catalysis:  Two Rhodium Centers vs. One Cobalt
DTSTART:20261013T140000
DTEND:20261013T150000
DTSTAMP:20261001T160713Z
UID:679c07c58910adf10f5a01713ee233709b05e0160de8966fda2f9351
CATEGORIES:Conferences - Seminars
DESCRIPTION:George G. Stanley\, Emeritus Professor\, LSU\nIn 1993 we repor
 ted a dirhodium tetraphosphine hydroformylation catalyst system that repre
 sented one of the best examples of bimetallic cooperativity in homogeneous
  catalysis (Science\, 1993\, 260\, 1784).  Understanding this catalyst sy
 stem turned out to be a long process of discovery and updated proposals on
  the nature of the catalyst (Angew. Chem. Int. Ed.\, 1996\, 35\, 2253\; JA
 CS\, 2003\, 125\, 11180).  Extensive in situ IR and NMR studies\, in conj
 unction with DFT calculations\, have finally shed light on what turns out 
 to be a far more complicated catalyst system spanning three different dirh
 odium catalysts with different charges\, oxidation states\, and reactiviti
 es.  The most active form of this catalyst\, [Rh2(m-H)2(CO)2(rac-Et\,Ph-P
 4)]2+\, has a significant fragmentation problem due to the tetraphosphine 
 ligand not chelating strongly enough.  A redesigned\, super-chelating tet
 raphosphine ligand initially appeared to solve the fragmentation problem a
 nd generated a more active and selective dirhodium hydroformylation cataly
 st.  This\, however\, had a new Rh-induced tetraphosphine cleavage side r
 eaction that led to catalyst deactivation.  Studies with a dicationic dic
 obalt tetraphosphine variant showed surprising hydroformylation activity u
 nder mild conditions for cobalt hydroformylation.  Studies clearly indica
 ted an absence of bimetallic cooperativity and a shift to much simpler mon
 ometallic analogs.  This new class of highly active cationic cobalt(II) b
 isphosphine catalysts have similar hydroformylation and alkene isomerizati
 on activity to HCo(CO)4\, but a far greater temperature/pressure stability
  range.  They are about 100 times more active relative to the neutral HCo
 (CO)3(PR3) catalysts used by Shell Chemical.  These high-spin Co(II) cata
 lysts have the general form: [HCo(CO)x(P2)](BF4)\, where x = 1-3\, and P2 
 = chelating bisphosphine.  Unlike all other hydroformylation catalysts kn
 own this new class has higher activity with electron-donating alkylated ph
 osphine ligands.  The high activity of these catalysts allow them to oper
 ate under far lower temperatures and pressures relative to HCo(CO)4 and HC
 o(CO)3(PR3).  They are especially effective at hydroformylating internal 
 branched alkenes to produce linear aldehydes (Science\, 2020\, 367\, 542\;
  JACS\, 2023\, 145\, 19715).\n 
LOCATION:CH G1 495 https://plan.epfl.ch/?room==CH%20G1%20495
STATUS:CONFIRMED
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