Gas Phase Formation, Structure and Reactivity of Gold Cluster Ions - Gold Clusters, Colloids and Nanoparticles - page 199

FT-ICRMS to investigate metal cluster ion-mediated bond coupling reaction between
CH 4 and NH 3 [ 317 ]. While Pt is a known catalyst for this reaction, Pt n + clusters ( n 2)

do not induce the C-N coupling step and the Au n + clusters do not activate the C-H
bond ( n 2). In contrast, the mixed metal cluster PtAu + was successful since it

combines the reactivity of both metals needed for each step (Eqs. ( 49 ) and ( 50 )).
Deuterium labelling confirmed that N-H bond activation occurs in the second step:

PtAu þ þ PtAuCH 2 þ CH 4 ! H 2 ð 49 Þ

þ þ

PtAuCH 2 þ

NH 2 ! ½ PtAuCH 3 N H 2 ð 50 Þ

In a follow-up study, the C-N coupling of methane and NH 3 was examined for
larger bimetallic platinum-gold cluster cations [ 282 ]. Unlike the heterodimer,
PtAuCH 2 + , which undergoes C-N bond coupling, Pt 2 AuCH 2 + reacts with NH 3
via carbide formation (Eq. ( 51 )), as does PtAu 2 CH 2 + (Eq. ( 52 )), which also
undergoes Au atom displacement (Eq. ( 53 )). The reactivity of the bare bimetallic
platinum-gold cluster cations towards ammonia and methylamine was also exam-
ined. The reactivity was found to depend on the nature of both the metal cluster and
the amine. For example, PtAu + reacts with NH 3 via displacement of Au (Eq. ( 54 )),
while for methylamine three channels are observed: hydride abstraction (Eq. ( 55 )),
dehydrogenation (Eq. ( 56 )) and double dehydrogenation (Eq. ( 57 )):

Þ þ þ

Pt 2 AuCH 2 þ

NH 3 ! Pt 2 AuC NH 3 ð H 2 ð 51 Þ

PtAu 2 CH 2 þ Þ þ þ NH 3 ! PtAu 2 CNH 3 ð H 2 ð 52 Þ

þ þ ! ½ ð Þ

PtAuCH 5 N Au 53

PtAu þ þ Þ þ þ NH 3 ! Pt NH 3 ð Au ð 54 Þ

PtAu þ þ NH 2 þ

CH 3 NH 2 ! CH 2 ¼

ð Þ

PtAuH 55

þ þ ! ½ PtAuCH 3 N H 2 ð 56 Þ

þ þ 2H 2 ! PtAuCHN ½ ð 57 Þ

The reactivity of bimetallic Pt x Au y + clusters ( x + y

4) towards O 2 and CH 4
highlights the role of cluster composition in controlling the preferred reaction
channel(s) [ 318 ]. While platinum-rich clusters behave similarly to Pt x + clusters,
gold-rich clusters like their pure gold counterparts are inert. For the oxygen
substrate, platinum-only and platinum-rich clusters react via cluster decomposition,
as illustrated for the trimer clusters in Eqs. ( 58 )-( 62 ). When methane is used as a
substrate, pure and platinum-rich clusters react via dehydrogenation (Eq. ( 63 )).
Indeed, this reaction only occurs for y 1. The carbene Pt x Au y CH 2 +

mainly loses H 2 upon CID (Eq. ( 64 )) and undergoes dehydrogenation in reactions
with a second molecule of methane (Eq. ( 65 )):

¼ 1 and x

Pt 3 þ Pt 2 þ O 2 ! PtO 2 ð 58 Þ

Pt 2 O þ þ

! PtO ð 59 Þ