1.3 The Catalytic Binuclear Elimination Reaction (CBER) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
1.4 In Situ Spectroscopic Investigations, Specialized Experimental Set-Ups,
Chemometrics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
1.5 Brief Comment: Graph Theory and Flows in Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
2 Connectivity of Catalytic Reaction Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
2.1 Variations on Unicyclic Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
2.2 Monometallic and Heterobimetallic CBER: The Core Mechanisms . . . . . . . . . . . . . . . 199
2.3 Monometallic and Heterobimetallic CBER: The Extended Mechanisms . . . . . . . . . . 201
2.4 Disjoint CBER + Unicyclic Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
2.5 Increased Synthetic Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208
2.6 Regio-, Chemo- and Stereoselectivities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210
2.7 Feinberg, Horiuti and Wegscheider Criterion . . . . .. . . . . . . . . . . . . .. . . . . . . . . . . . . .. . . . . . . 211
2.8 Other Systems, Other Non-linear Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
3 The Catalytic Binuclear Elimination Reaction . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . .. . . . . . . . 219
3.1 Chemistry, Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
3.2 In Situ FTIR Spectra and Kinetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220
3.3 Isotopic Labelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222
3.4 From Stoichiometric to Catalytic Binuclear Reaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223
3.5 Miscellaneous Mechanistic Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
3.6 Possible Future Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226
4 Conclusions . . . .. . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . .. . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . 227
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
1 Introduction
1.1 Catalytic Syntheses, Cooperativity and Synergism
In the catalytic sciences, and specifically in the context of organic synthesis, it is
common to represent the catalytic transformation of reactants, namely, reagents
(substrate(s)) to product(s) as shown in Fig. 1a. This simplified representation puts
emphasis on the net transformation of reactants, which is indeed the proper emphasis
for the vast majority of synthetic situations. In Fig. 1a, the details of the catalysis are
embedded in the term [cat], and the details are in no manner explicit. Therefore, in
fine heterogeneous catalysis [cat] is simply understood to be a heterogeneous catalyst,
perhaps a supported metal added to the system [1], in enzymatic catalysis [cat] is
usually understood to be a protein or metalloprotein added to the system [2], in
organocatalysis [cat] is often understood to be an organic amine or phosphine added
to the system [3], in acid/base catalysis [cat] may refer to H
+ or OH
À in the system or
Lewis acids/bases [4], and in metal-mediated homogeneous catalysis, [cat] often
refers to an inorganic or organometallic precursor added to the system [5].
On occasion, there is a secondary interpretation or meaning used for [cat] and
that is the actual catalytic mechanism by which the reaction is effected or accelerated. It is this secondary meaning that will form the basis for the present exposition.
In order to keep the reaction diagrams as simple and clear as possible in the present
contribution, green boxes will always represent reagents (substrate(s)) and red
188
M. Garland
1.4 In Situ Spectroscopic Investigations, Specialized Experimental Set-Ups,
Chemometrics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
1.5 Brief Comment: Graph Theory and Flows in Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
2 Connectivity of Catalytic Reaction Networks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
2.1 Variations on Unicyclic Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
2.2 Monometallic and Heterobimetallic CBER: The Core Mechanisms . . . . . . . . . . . . . . . 199
2.3 Monometallic and Heterobimetallic CBER: The Extended Mechanisms . . . . . . . . . . 201
2.4 Disjoint CBER + Unicyclic Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
2.5 Increased Synthetic Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208
2.6 Regio-, Chemo- and Stereoselectivities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210
2.7 Feinberg, Horiuti and Wegscheider Criterion . . . . .. . . . . . . . . . . . . .. . . . . . . . . . . . . .. . . . . . . 211
2.8 Other Systems, Other Non-linear Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
3 The Catalytic Binuclear Elimination Reaction . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . .. . . . . . . . 219
3.1 Chemistry, Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
3.2 In Situ FTIR Spectra and Kinetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220
3.3 Isotopic Labelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222
3.4 From Stoichiometric to Catalytic Binuclear Reaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223
3.5 Miscellaneous Mechanistic Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
3.6 Possible Future Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226
4 Conclusions . . . .. . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . . . . . . . .. . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . 227
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
1 Introduction
1.1 Catalytic Syntheses, Cooperativity and Synergism
In the catalytic sciences, and specifically in the context of organic synthesis, it is
common to represent the catalytic transformation of reactants, namely, reagents
(substrate(s)) to product(s) as shown in Fig. 1a. This simplified representation puts
emphasis on the net transformation of reactants, which is indeed the proper emphasis
for the vast majority of synthetic situations. In Fig. 1a, the details of the catalysis are
embedded in the term [cat], and the details are in no manner explicit. Therefore, in
fine heterogeneous catalysis [cat] is simply understood to be a heterogeneous catalyst,
perhaps a supported metal added to the system [1], in enzymatic catalysis [cat] is
usually understood to be a protein or metalloprotein added to the system [2], in
organocatalysis [cat] is often understood to be an organic amine or phosphine added
to the system [3], in acid/base catalysis [cat] may refer to H
+ or OH
À in the system or
Lewis acids/bases [4], and in metal-mediated homogeneous catalysis, [cat] often
refers to an inorganic or organometallic precursor added to the system [5].
On occasion, there is a secondary interpretation or meaning used for [cat] and
that is the actual catalytic mechanism by which the reaction is effected or accelerated. It is this secondary meaning that will form the basis for the present exposition.
In order to keep the reaction diagrams as simple and clear as possible in the present
contribution, green boxes will always represent reagents (substrate(s)) and red
188
M. Garland