Introduction to New Trends in Cross-Coupling - New Trends in Cross-Coupling: Theory and Applications - page 5

long-lived catalyst. The TON can be calculated by dividing the amount of
reactant (moles) by the amount of catalyst (moles):

TON ¼ number of moles ð equivalents Þ of reactant
number of moles ð equivalents Þ of catalyst

This assumes a yield of the product of 100%, which is most often not the
case. To calculate the true number of turnovers, the yield obtained needs to
be taken into account. For example, if 10 mol of reactant and 2.5 mol of
catalyst are used, then the TON becomes

TON ¼ 10

2 : 5 ¼ 4

If the yield of the product is 94%, then the actual number of turnovers is

Actual TON ¼ 4 0.94 ¼ 3.76

Authors often report mole % of catalyst used. This refers to the fraction of
catalyst used relative to the amount of limiting reactant present.

1.2.2 Turnover Frequency (TOF)
Turnover frequency is defined as the number of passes through the catalytic
cycle per unit time (typically seconds, minutes or hours). This number is
usually determined by dividing the TON by the time required to produce the
given amount of product.
However, as with the TON, the actual yield of the product also needs to be
taken into account. Continuing the example above, if the reaction in ques-
tion was run for 7 h to obtain the 94% yield, the TOF is

TOF ¼ 3 : 76 turnovers
7h

¼ 0 : 54 h 1

1.3 General Elementary Steps
The generally accepted simplified catalytic cycle for cross-coupling reactions is
shown in Scheme 1.1, where L n Pd(0), the active catalytic species, acts as a
''matchmaker''. In Japanese language, ''catalyst'' is pronounced shoku bai and
in Chinese it is chu mei (the same character as for matchmaker). 6
In C-C bond-forming cross-coupling, there are two coupling partners: an
aryl/vinyl halide or pseudohalide and an organometallic reagent such as a
Grignard reagent. There are three basic steps in the catalytic cycle: oxidative
addition, transmetallation and reductive elimination.
Here is an analogy: one of the partners with a family member or friend
(R-X) establishes a connection with the matchmaker [L n Pd(0)] with the
profile of ''R''. This is called the oxidative addition of an organic halide/