reaction rate and total TON after 9 h (Table 2) [41]. Complex 13 could also catalyze
the dehydrogenation of n-undecane with slightly higher efficiency than 15 and 16.
The structurally more rigid 1-adamantyl-substituted PCP pincer complex 14 was
more stable than complexes 8 and 16 during the catalytic dehydrogenation of
cyclodecane [42]. Although the initial rate of 14-catalyzed cyclodecane dehydrogenation was lower than that observed for t-butyl- or isopropyl-substituted complexes
8 and 16 at reaction times of <3 h, the total TON exceeded those of 8 and 16 after
24 h (Table 3). A similar trend was also observed for the dehydrogenation of ndodecane (bp 216
C), in which case a TON of 71 was reached after 72 h.
Anthracene-based PCP pincer Ir complex 17 features a much more rigid backbone than m-xylene-based complexes and should therefore exhibit a higher thermal
stability [43]. This complex catalyzed the acceptorless dehydrogenation of
cyclododecane (bp 244
C) to a mixture of cis- and trans-cyclododecene (1:2.4)
even at 250
C, achieving an initial TOF of 40 h
À1 and a TON of 136 after 148 h. At
230
C, the catalytic performance decreased to an initial TOF of 30 h
À1 and a TON of
126 after 192 h. Thus, the rigidness and steric bulk of 17 effectively increased
Table 2 Comparison of the catalytic performances of Ir complexes 13, 15, and 16 for the
acceptorless dehydrogenation of cyclodecane
Ir cat.
Time (h)
cis-CDE
trans-CDE
DEC
Total
13
1
388
65
36
489
9
807
163
119
1,089
15
1
49
49
3
101
9
325
72
11
408
16
1
153
31
12
196
9
410
86
96
592
TONs are shown
CDE cyclodecene, DEC diethylcyclohexane
Table 3 Comparison of the
catalytic activities of Ir complexes 8, 14, and 16 for the
acceptorless dehydrogenation
of cyclodecane
Total cyclodecene (mM)
Time (h)
Ir cat. 14
Ir cat. 8
Ir cat. 16
1
74
102
136
3
179
218
274
5
251
240
–
24
509
267
364
48
526
294
–
72
534
305
366
96
543
314
–
Conditions: [catalyst] ¼ 1.0 mM, cyclodecane volume ¼ 1.5 mL.
Oil bath temperature ¼ 230
C
Iridium-Catalyzed Dehydrogenative Reactions
9