Complex sentence: Fearing reprisals from Venice in Negroponte, and loath to antagonize the rest of Frankish Greece, when the permanence of the Catalan regime was still uncertain, Boniface declined the honour and the Catalans instead chose another Frankish captive lord, Roger Deslaur, as their leader.
Split into simpler sentences: Fearing reprisals from Venice in Negroponte, and loath to antagonize the rest of Frankish Greece, when the permanence of the Catalan regime was still uncertain, Boniface declined the honour. Consequently the Catalans instead chose another Frankish captive lord, Roger Deslaur, as their leader.